CN108256287B - Calculation method for improving photocatalytic property of ZnO (0001) surface by doping and adsorbing Fe atoms - Google Patents

Calculation method for improving photocatalytic property of ZnO (0001) surface by doping and adsorbing Fe atoms Download PDF

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CN108256287B
CN108256287B CN201810031620.XA CN201810031620A CN108256287B CN 108256287 B CN108256287 B CN 108256287B CN 201810031620 A CN201810031620 A CN 201810031620A CN 108256287 B CN108256287 B CN 108256287B
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王平
程静思
何静芳
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Abstract

The invention discloses a calculation method for improving the photocatalytic property of ZnO (0001) surface by doping and adsorbing Fe atoms, which comprises the following steps: constructing an original cell of a ZnO material in MS software, optimizing the structure, and then constructing a ZnO (0001) surface super-cell and a doping and adsorption model of Fe atoms at different sites on the surface of pure ZnO (0001); performing structure optimization and GGA + U method calculation on the surface of the material, selecting energy band structure, state density, optical property and respectively corresponding precision, and calculating each model; analyzing each model by using a CASSTEP module to obtain the formation energy, the optical property constant and the work function of the ZnO (0001) surface doped and adsorbed with Fe atoms and obtain the electronic structure and the optical property corresponding to each model. Thereby improving the photocatalytic activity of the ZnO (0001) surface in the visible light range and providing a certain reference for the practical application of ZnO photocatalysis.

Description

Calculation method for improving photocatalytic property of ZnO (0001) surface by doping and adsorbing Fe atoms
Technical Field
The invention relates to the research field of improving the photocatalytic property of the surface of ZnO (0001), and a method for calculating the electronic structure and the optical property of a ZnO (0001) surface system doped and adsorbed by Fe by adopting a density functional-based CAStep module in MS software. The method is characterized in that a ZnO (0001) surface doping and adsorption model is established by Fe atoms, the electronic structure and the optical property of each Fe-doped and adsorbed ZnO (0001) surface model are calculated by using a CAStep module, the internal mechanism of the photocatalytic property is researched by combining an energy band theory and an electronic transition theory, and a certain reference is provided for the practical application of ZnO photocatalysis.
Background
At present, environmental pollution and energy crisis become one of the major problems affecting human life, and photocatalysts using semiconductor materials as media attract extensive attention due to their great application potential in the aspect of pollutant degradation. The ZnO semiconductor material is distinguished in numerous photocatalytic semiconductor materials due to high photosensitivity and biocompatibility, low cost, exciton binding energy up to 60meV, low dielectric constant, large photoelectric coupling rate, high chemical stability and other good performances. Particularly, the photocatalytic technology based on the wide bandgap ZnO semiconductor photocatalytic material has the advantages of low energy consumption, high efficiency, mild reaction conditions, capability of reducing secondary pollution and the like, and arouses high attention of people. However, in practical application, the defects that the sunlight utilization rate is low, the catalytic activity is reduced due to the recombination of photon-generated carriers, the catalyst is difficult to recycle and the like exist, and the further development of the catalyst is limited.
In recent years, people expand the spectral response range of ZnO by introducing impurities, defects or changing the morphology of ZnO and the like, theoretical calculation shows that in four low miller index surfaces, Zhang Hai Feng et al in 2013 show that the ZnO (0001) surface has the highest photocatalytic activity in the visible light range, and further discovers that the adsorption of Si atoms on the ZnO (0001) surface can enhance the utilization of sunlight in the next year, L ahmer researches noble metal Ag atoms on ZnO nonpolar Ag atoms in 2016
Figure BDA0001546683180000021
The result of the photocatalysis mechanism of adsorption on the surface shows that Ag atoms are adsorbed in a visible light range to generate a new absorption peak so as to enhance the photocatalysis activity of the ZnO surface. So far, experiments and theories have reported that the Fe atom doped ZnO nano crystal enhances the photocatalytic activity to improve the degradation rate of organic matters, but the photocatalytic mechanism of the doping and adsorption of Fe atoms on the surface of ZnO (0001) has not been researched.
Disclosure of Invention
The invention aims to provide a calculation method for improving the photocatalytic property of ZnO (0001) surface light by Fe atom doping and adsorption, which is characterized in that a supercell model of the ZnO (0001) surface doped and adsorbed by Fe atoms is constructed by MS software, a CAStep module in the supercell model is used for calculating the structural stability, electronic structure and light absorption spectrum of the supercell model doped and adsorbed by Fe atoms, the calculation result is drawn and analyzed by Origin drawing software, and the photocatalytic property of the supercell model is researched by the influence of an electronic transition mechanism in an electronic structure on a light absorption coefficient.
The CAStep software package adopted by the invention is one of the ab initio quantum mechanics software packages specially designed for solid materials science, and the plane wave pseudopotential method under the density functional theory is adopted to carry out first-nature principle simulation calculation on the crystal and the surface characteristics of the crystal. The constructed material systems are calculated by determining the calculation parameters, and the output file is analyzed, so that the geometric structure, the electronic structure, the optical characteristics and the like corresponding to the material systems can be researched to obtain the required results.
The purpose of the invention is realized by the following technical scheme.
The invention provides a calculation method for improving the photocatalytic property of ZnO (0001) surface by doping and adsorbing Fe atoms based on theoretical calculation of a first principle, which comprises the following steps:
1) building models
1a) Constructing an original cell of a ZnO body material in Materials Studio software, and carrying out structural optimization on the original cell;
1b) constructing a super-cell model of the surface of ZnO (0001) formed by five Zn-O double atomic layers by using the optimized ZnO body material primitive cell obtained in the step 1 a);
1c) establishing ZnO (0001) surface super cell models corresponding to different Fe atom doping sites and adsorption sites on the basis of the ZnO (0001) surface super cell model obtained in the step 1 b).
2) Theoretical calculation of
2a) Selecting and setting appropriate calculation parameters, performing structural optimization on the super cell model with Fe atom doping and adsorption and pure ZnO (0001) surface structure obtained in the steps 1b) and 1c) by using a GGA method, adding corresponding coulomb correction value U values to atoms of different types in the model, and performing total energy calculation on the super cell model by using a GGA + U method;
2b) based on the super cell of energy calculation, the band structure, state density and optical properties, and their respective corresponding accuracies are selected to calculate each model.
3) Analysis results
And analyzing the properties of the calculated ZnO surface models by using a CAStep module to obtain the formation energy and optical property constant of the doping and adsorption ZnO (0001) surface super-cell model of the Fe atom and the work function of the Fe atom adsorption ZnO (0001) surface, and drawing an electronic structure and an optical property diagram corresponding to each model, thereby obtaining the structural stability and the change of the electronic structure of the doping and adsorption ZnO (0001) surface of the Fe atom, and the influence of the doping and adsorption of the Fe atom on the optical property and the photocatalytic property of the ZnO (0001) surface.
For the above technical solution, the present invention also has a further defined solution:
in the step 1b), the construction method of the super cell model for the surface of ZnO (0001) is as follows:
a. slicing the optimized ZnO body material primitive cell obtained in the step 1a) along a plane formed by an X axis and a Y axis of the ZnO body material primitive cell, and establishing a ZnO crystal face with the thickness of 5 Zn-O double atomic layers;
b. introducing a thickness of
Figure BDA0001546683180000042
The vacuum layer forms a three-dimensional ZnO (0001) surface structure, two Zn-O double atomic layers at one side far away from the vacuum layer are fixed to simulate a bulk material, and three layers close to the vacuum layer are allowed to relax to study the surface characteristics;
c. to prevent non-physical charge transfer between the top and bottom layers, the dangling bonds of the oxygen atoms of the bottom layer on the side away from the vacuum layer are saturated with a pseudohydrogen having a charge of 0.5e or 1.5 e.
In the step 1c), establishing ZnO (0001) surface super-cell models corresponding to different Fe atom doping sites and adsorption sites, wherein the doping positions are Zn atoms located in a first layer, a second layer and a third layer of the surface of ZnO (0001) and octahedral interstitial positions formed by the Zn atoms; three highly symmetrical sites of the ZnO (0001) surface structure are selected to construct an adsorption model.
In step 2a), selecting and setting appropriate calculation parameters includes: pseudopotentials for describing the interaction potential between the real and valence electrons of an ion, approximation methods and correction functionals for describing and correcting the exchange correlation energy, the convergence accuracy of the energy, self-consistent field and energy band used in the iterative process, the maximum force, maximum energy band acting on each atomInternal stress and tolerance drift of; plane wave cut-off energy EcutThe Brillouin zone k point and the selection of different configuration coulomb correction value U values corresponding to each atom in the coulomb correction method.
In the step 3), the formation energy E of the ZnO (0001) surface super cell model by doping and adsorbing Fe atoms is realized by the following formulafThe calculation of (2):
Figure BDA0001546683180000041
wherein: etotTotal energy of the surface system containing defects, EslabTotal energy of pure ZnO (0001) surface, niIs the number of atoms of type i, where n is the number of atoms i removed from the unit celli<0, or when atom i is added from the unit cell ni>0；μiIs the chemical potential of a single i atom.
In the step 3), the calculation of the optical property constant of the ZnO (0001) surface doped and adsorbed with Fe atoms is realized by the following formula:
a. the optical properties of materials studied using the first principle of linearity are mainly introduced by the dielectric function, in the linear response range, the macroscopic optical response function of a solid is usually described by the complex dielectric constant (ω) of light;
b. imaginary part of dielectric function2(ω) is calculated from the matrix elements between the electronic wave functions of the occupied and unoccupied states; and real part1(ω) from the imaginary part using the Kramers-Kronig relationship2(omega) is obtained by calculation;
c. the optical property constants of the material, namely the absorption coefficient α (omega), the reflectivity R (omega), the refractive index n (omega) and the energy loss spectrum L (omega) can be formed by1(ω) and2(ω) was derived.
In the step 3), the work function of the ZnO (0001) surface adsorbed by the Fe atom is solved through the following formula:
Wf＝Evac-EF(9)
in the formula, EvacIs a vacuum level, EFIs the fermi level.
According to the invention, the calculation results of Fe atom doping and adsorption and pure ZnO (0001) surface super-cell models are calculated by a GGA + U method, and the differences of the geometrical structure, the structural stability, the electronic structure and the light absorption spectrum between the ZnO (0001) surface model doped and adsorbed with Fe atoms and the pure ZnO (0001) surface model can be contrastively analyzed. The geometric structure and the formation energy can be compared and analyzed through the calculation result and the formation energy calculation formula, the energy band structure chart, the state density chart, the light absorption spectrum and the like of each system are obtained, drawing is performed by means of Origin function drawing software, and the method is favorable for clearly obtaining the rule. The forbidden band width (E) of each ZnO surface system can be obtained by analyzing the energy band structure and the state densityg) Whether the material is a direct band gap semiconductor, the specific orbital composition of a conduction band and a valence band and the transition law of electrons are helpful for researching the mechanism of enhancing the photocatalytic property by doping or adsorbing Fe atoms. In addition, a dielectric function diagram, an optical absorption spectrum, an optical reflection spectrum, a light refraction spectrum, an energy loss spectrum, and the like of each ZnO (0001) surface super cell model obtained by optical characteristic calculation are shown. In the present study, the light absorption spectra of the systems and the effect of doping and adsorption of Fe atoms on the photocatalytic properties of ZnO (0001) surfaces were mainly focused.
The implementation of the method of the invention has the following beneficial effects:
1) the invention provides a calculation method for improving the photocatalytic property of ZnO (0001) surface light by Fe atom doping and adsorption, which has accurate calculation result by utilizing the first principle of GGA + U, can provide theoretical support for relevant experiments, and provides certain reference for practical application of ZnO photocatalysis.
2) The method has the advantages of low cost and no pollution, and saves manpower and material resources.
3) The invention establishes a ZnO (0001) surface super-cell model doped and adsorbed with Fe atoms, and the calculation result shows that the addition of Fe atoms obviously enhances the light absorption coefficient of the ZnO (0001) surface in a visible light region, thereby being beneficial to the implementation of a photocatalytic reaction.
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In order to more clearly illustrate the technical solution of the method of the present invention, the drawings used in the present specification will be briefly described below.
FIG. 1 is a flow chart of a calculation method for improving photocatalytic properties of ZnO (0001) surface by doping and adsorbing Fe atoms according to the invention;
FIGS. 2 (a) and (b) are respectively a geometrical structural view of the surface of ZnO (0001);
FIGS. 3(a) - (d) are the respective geometrical structural diagrams of the surface of each Fe atom-doped ZnO (0001);
FIGS. 4(a) - (d) are respectively the structure diagrams of the energy bands of the surface of each Fe atom-doped ZnO (0001);
FIGS. 5(a) - (d) are respectively a state density diagram of the surface of each Fe atom-doped ZnO (0001);
FIGS. 6(a) - (c) are respectively the geometrical structural views of the surface of each Fe atom adsorbed to ZnO (0001);
FIGS. 7(a) to (c) are respectively energy band structural diagrams in which each Fe atom adsorbs to the surface of ZnO (0001);
FIGS. 8(a) - (c) are graphs of the density of states in which each Fe atom adsorbs to the surface of ZnO (0001), respectively;
FIGS. 9(a) - (d) are electrostatic potential distribution diagrams of each Fe atom adsorbing to the surface of ZnO (0001), respectively;
fig. 10(a) and (b) are surface light absorption spectra of each Fe atom doped and adsorbed ZnO (0001), respectively.
Detailed Description
To further clarify the objects and advantages of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. The steps of the calculation method for improving the photocatalytic property of the ZnO (0001) surface by doping and adsorbing Fe atoms are shown in figure 1:
step 1 construction of a model
1a) ZnO belongs to a hexagonal wurtzite structure and a space group P63mc, lattice constant:
Figure BDA0001546683180000071
Figure BDA0001546683180000072
α is β is 90 DEG, gamma is 120 DEG, and its primitive cell is composed of two Zn atoms and two O atoms, and is based on the above normal temperature and pressureAnd (3) constructing an original cell model of the ZnO bulk material by using a Materials Visualizer module in the MS according to the stable phase parameters and the periodic boundary conditions of the lower ZnO bulk material, and performing structural optimization on the original cell model.
1b) After the ZnO cell is subjected to structural optimization and total energy calculation, the optimized ZnO cell is sliced, and a super cell model of a ZnO (0001) surface composed of five Zn — O diatomic layers is constructed, as shown in fig. 2 (a) and (b), the detailed steps are as follows:
a. slicing the optimized ZnO body material primitive cell obtained in the step 1a) along a plane formed by an X axis and a Y axis of the ZnO body material primitive cell, and establishing a ZnO crystal face with the thickness of 5 Zn-O double atomic layers;
b. to eliminate the interaction between adjacent surfaces, a thickness of
Figure BDA0001546683180000081
To
Figure BDA0001546683180000082
The vacuum layer forms a three-dimensional ZnO (0001) surface structure, two Zn-O double atomic layers at one side far away from the vacuum layer are fixed to imitate a bulk material, and three layers close to the vacuum layer are allowed to be freely relaxed to study the surface characteristics;
c. to prevent non-physical charge transfer between the top and bottom layers, the dangling bonds of the oxygen atoms of the bottom layer on the side away from the vacuum layer are saturated with a pseudohydrogen having a charge of 0.5e or 1.5 e.
1c) The super cell model of Fe atom doped and adsorbed on the surface of ZnO (0001) is established on the basis of the super cell model of ZnO (0001) surface obtained in step 1 b). Because the three Zn-O double atomic layers on the surface are allowed to relax freely in calculation, Fe atoms are doped in different Zn atom positions of the first layer, the second layer and the third layer of the surface counted from the direction close to the vacuum layer and are respectively marked as P1、P2And P3In addition, the doping may enter interstitial sites (considering the central position of the Fe atom in the octahedron formed by Zn atoms) and is noted as PiZnO (0001) surface super cell with four Fe atom doping positions after structure optimizationThe model is shown in FIGS. 3(a) - (d). For the adsorption of a single Fe atom on the ZnO (0001) surface, three highly symmetric adsorption points on the ZnO (0001) surface are mainly considered, including face-centered vacancies (H)3) Apical position of O atom (T)4) And Zn atom Top position (Top), and the adsorption model after structure optimization is shown in FIGS. 6(a) - (c).
Step 2 theoretical calculation
2a) Selecting and setting appropriate calculation parameters, performing structural optimization on the Fe atom doping and adsorption obtained in the steps 1b) and 1c) and the super cell model with the pure ZnO (0001) surface structure by using a GGA method, adding corresponding coulomb correction value U values to atoms of different types in the model, and performing total energy calculation on the super cell model by using a GGA + U method.
Wherein, selecting and setting appropriate calculation parameters comprises: describing the pseudopotential used for the interaction potential between the ion real and valence electrons, describing and correcting the approximation method and correction functional of the exchange correlation energy, the energy, self-consistent field and convergence accuracy of the energy band adopted in the iterative process, the maximum force acting on each atom, the maximum internal stress and the tolerance deviation; valence electron configuration of each element, plane wave cut-off energy EcutThe k point of the Brillouin zone and the U values corresponding to different configurations of atoms in the GGA + U coulomb correction method. The interaction potential between ion real and valence electrons is described by adopting an ultra-soft pseudopotential, the exchange correlation between electrons and electrons can be selected from Generalized Gradient Approximation (GGA), and is corrected by utilizing an exchange correlation gradient correction functional proposed by PBE (photon beam ionization) method, in order to avoid the problem that the band gap is underestimated by the GGA method, the study adds the repulsion action of spin electrons on different orbits as an energy term Hubbard U, and the total energy and the properties of each model are calculated by adopting a GGA + U correction method. The valence electron configuration of each element is Zn 3d 104s2, O 2s 22p4, Fe 3d 64s2The path of the brillouin zone k point is set as-a- Η -k- Μ -L-h.
Figure BDA0001546683180000091
2b) According to the calculation parameters selected in the step 2a), the energy band structure, the state density, the optical properties and the like are selected, and the accuracy corresponding to the energy band structure, the state density, the optical properties and the like is respectively selected, and the ZnO (0001) surface models established in the steps 1b) and 1c) are respectively calculated by operating a CAStep module.
Step 3 analysis of the results
And analyzing the properties of the calculated ZnO surface models by using a CAStep module to obtain the formation energy and optical property constant of the ZnO (0001) surface super-cell model doped and adsorbed with Fe atoms and the work function of the ZnO (0001) surface adsorbed with the Fe atoms.
Formation energy E for realizing doping of Fe atoms and adsorption of ZnO (0001) surface super cell modelfCalculated by the following formula:
Figure BDA0001546683180000101
wherein: etotTotal energy of the surface system containing defects, EslabTotal energy of pure ZnO (0001) surface, niIs the number of atoms of type i, where n is the number of atoms i removed from the unit celli<0, or when atom i is added from the unit cell ni>0；μiIs the chemical potential of a single i atom.
The optical property constants of the surfaces of the ZnO (0001) doped and adsorbed by Fe atoms are obtained by the following methods:
a. the optical properties of materials studied using the first principle of linearity are mainly introduced by the dielectric function, in the linear response range, the macroscopic optical response function of a solid is usually described by the complex dielectric constant (ω) of light:
(ω)＝1(ω)+i2(ω) (2)
wherein: ω represents the frequency of the frequency,1(ω) and2(ω) represents the real and imaginary parts of the dielectric function, respectively;
b. imaginary part of dielectric function in the above equation2(ω) is directly related to the optical absorption, which can be determined by the choice of the electronic transitions, the moment between the electronic wave functions of the occupied and unoccupied statesArray element calculation obtains:
Figure BDA0001546683180000102
wherein: omega is the unit cell volume, is the dirac function,0the dielectric constant in vacuum, c and v are the conduction band and the valence band, respectively, k is the reciprocal lattice vector,
Figure BDA0001546683180000103
and
Figure BDA0001546683180000104
intrinsic energy levels in the conduction and valence bands, respectively, u is the vector defining the polarization of the incident electric field, r is the position vector,
Figure BDA0001546683180000105
and
Figure BDA0001546683180000106
the wave functions of the conduction and valence bands, respectively.
And real part1(ω) from the imaginary part using the Kramers-Kronig relationship2(ω) is calculated as:
Figure BDA0001546683180000111
wherein: p is the principal value of the integral;
c. the optical property constants of the material can be determined by1(ω) and2(ω) is derived as:
absorption coefficient α (ω):
Figure BDA0001546683180000112
reflectance R (ω):
Figure BDA0001546683180000113
refractive index n (ω):
Figure BDA0001546683180000114
energy loss spectrum L (omega)
Figure BDA0001546683180000115
Work function W of Fe atom adsorbing ZnO (0001) surfacefThe solution is made according to the following formula:
Wf＝Evac-EF(9)
in the formula, EvacIs a vacuum level, EFIs the fermi level.
And drawing an electronic structure and an optical property graph corresponding to each model, thereby obtaining the structural stability and the change of the electronic structure of the ZnO (0001) surface doped and adsorbed by the Fe atom, and the influence of the doping and the adsorption of the Fe atom on the optical property and the photocatalytic property of the ZnO (0001) surface.
The ZnO (0001) surface geometry after the optimized and stable Fe atom doping and adsorption is shown by Materials Visualizer in MS, as shown in FIGS. 3(a) - (d) and FIGS. 6(a) - (c), and the calculation result is used for analyzing the change of bond length and distance between atoms in and between layers of the surface which can be freely relaxed; the total energy of each system can be obtained from the calculation result obtained by the GGA + U method, and the structural stability of each system can be analyzed by calculation according to a formation energy formula. The formation energy is one of important bases for judging the stability of an ordered structure system, the formation energy is negative and the smaller the formation energy, the more stable the system structure, and the easier the doping or adsorption of Fe atoms on the surface of ZnO (0001).
The band structure and state density of a ZnO (0001) surface system doped and adsorbed by Fe are comprehensively analyzed by combining valence electron configurations of Zn, O and Fe elements, the doping system is shown in figures 4(a) - (d) and figures 5(a) - (d), the adsorption system is shown in figures 7(a) - (c) and figures 8(a) - (c), the forbidden bandwidth, the relative position of the Fermi level and the band structure, the transition mode of electrons and the like of each system can be obtained by comprehensively analyzing the band structure by using Origin, the surface state generated due to surface unsaturated dangling bonds can be seen by analyzing the layered state density (L PDOS) of a pure ZnO (0001) surface and the contribution of electron orbitals of different atoms to the total state density can be seen by analyzing the band structure and the state density of the ZnO (0001) surface system doped and adsorbed by Fe atoms, the band structure and the state density of the adsorbed ZnO (0001) surface system are compared with the pure ZnO (0001) surface system, the addition of Fe atoms enables the electron structure of the system to have upper and lower spin potential and the electron orbitals of the Fe atoms to have a significant influence on the ZnO (0001) surface state density and the ZnO (0001) surface system, and the electron structure of the adsorption system can also be obtained by analyzing one of the electrostatic work function distribution of the surface (0001) surface system, and the energy distribution of the Fe atom can be obtained by analyzing the electrostatic surface system can be represented by one of the electrostatic work function distribution of the surface (0001) of the surface.
The light absorption spectrum can be obtained by calculating the optical characteristics, the photocatalytic characteristics of the semiconductor material are directly related to the light absorption coefficient, when light with a certain wavelength is radiated, photoproduction electrons and holes can be generated in the energy band of the n-type semiconductor photocatalyst, and the n-type semiconductor photocatalyst reacts with oxygen and water to generate superoxide ion free radicals (O2-) and hydroxyl free radicals (OH) with strong oxidizing property, and can react with organic matters adsorbed on the surface to degrade the organic matters into CO2、H2O and harmless inorganic substances such as inorganic salts are removed. Therefore, as shown in fig. 10(a), (b), the light absorption coefficient of the ZnO (0001) surface doped and adsorbed with Fe atoms is greatly enhanced in the visible light range compared to that of the pure ZnO (0001) surface, thereby contributing to enhancement of the photocatalytic activity of the ZnO surface.

Claims (6)

1. A calculation method for improving photocatalytic properties of ZnO (0001) surface by doping and adsorbing Fe atoms is characterized by comprising the following steps:
1) building models
1a) Constructing an original cell of a ZnO body material in Materials Studio software, and carrying out structural optimization on the original cell;
1b) constructing a super-cell model of the surface of ZnO (0001) formed by five Zn-O double atomic layers by using the optimized ZnO body material primitive cell obtained in the step 1 a);
1c) establishing ZnO (0001) surface super cell models corresponding to different Fe atom doping sites and adsorption sites on the basis of the ZnO (0001) surface super cell model obtained in the step 1 b);
in the step 1c), establishing ZnO (0001) surface super-cell models corresponding to different Fe atom doping sites and adsorption sites, wherein the doping positions are Zn atoms located in a first layer, a second layer and a third layer of the surface of ZnO (0001) and octahedral interstitial positions formed by the Zn atoms; selecting three highly symmetrical sites of a ZnO (0001) surface structure to construct an adsorption model;
2) theoretical calculation of
2a) Selecting and setting appropriate calculation parameters, performing structure optimization on the ZnO (0001) surface super cell models corresponding to the Fe atom doping sites and the adsorption sites obtained in the steps 1b) and 1c) and the super cell models of pure ZnO (0001) surface structures by using a GGA method, adding corresponding coulomb correction value U values to different types of atoms in the models, and performing total energy calculation on the super cell models by using a GGA + U method;
2b) on the basis of a super cell for energy calculation, selecting energy band structures, state densities and optical properties and corresponding accuracies respectively, and calculating each model by operating a CAStep module;
3) analysis results
And analyzing the properties of each calculated ZnO surface super cell model by using a CAStep module to obtain the formation energy and optical property constant of the Fe atom doped and adsorbed ZnO (0001) surface super cell model and the work function of the Fe atom adsorbed on the ZnO (0001) surface, and drawing an electronic structure and optical property diagram corresponding to each model, thereby obtaining the structural stability and the change of the electronic structure of the Fe atom doped and adsorbed ZnO (0001) surface, and the influence of the doping and adsorption of the Fe atom on the optical property and the photocatalytic property of the ZnO (0001) surface.
2. The calculation method for improving the photocatalytic property of the surface of ZnO (0001) by doping and adsorbing Fe atoms according to claim 1, wherein in the step 1b), the construction method for the super cell model of the surface of ZnO (0001) is as follows:
a. slicing the optimized ZnO body material primitive cell obtained in the step 1a) along a plane formed by an X axis and a Y axis of the ZnO body material primitive cell, and establishing a ZnO crystal face with the thickness of 5 Zn-O double atomic layers;
b. introducing a thickness of
Figure FDA0002493886800000021
The vacuum layer forms a three-dimensional ZnO (0001) surface structure, two Zn-O double atomic layers at one side far away from the vacuum layer are fixed to simulate a bulk material, and three layers close to the vacuum layer are allowed to relax to study the surface characteristics;
c. to prevent non-physical charge transfer between the top and bottom layers, the dangling bonds of the oxygen atoms of the bottom layer on the side away from the vacuum layer are saturated with a pseudohydrogen having a charge of 0.5e or 1.5 e.
3. The method for calculating the improvement of the photocatalytic property of the surface of ZnO (0001) by doping and adsorbing Fe atoms according to claim 1, wherein the step 2a) of selecting and setting the proper calculation parameters comprises the following steps: describing the pseudopotential used for the interaction potential between the ion real and valence electrons, describing and correcting the approximation method and correction functional of the exchange correlation energy, the convergence accuracy of the energy, self-consistent field and energy band adopted in the iterative process, the maximum internal stress and tolerance deviation acting on each atom; plane wave cut-off energy EcutThe Brillouin zone k point and the selection of different configuration coulomb correction value U values corresponding to each atom in the coulomb correction method.
4. The method for calculating the property of improving the photocatalytic property of the surface of ZnO (0001) by doping and adsorbing Fe atoms according to claim 1, wherein in the step 3), the forming energy E of the super cell model of the surface of ZnO (0001) by doping and adsorbing Fe atoms is realized by the following formulafThe calculation of (2):
Figure FDA0002493886800000031
wherein: etotTotal energy of the surface system containing defects, EslabTotal energy of pure ZnO (0001) surface, niIs the number of atoms of type i, where n is the number of atoms i removed from the unit celli<0, or when atom i is added from the unit cell ni>0；μiIs the chemical potential of a single i atom.
5. The calculation method for improving the photocatalytic property of the surface of ZnO (0001) by doping and adsorbing Fe atoms according to claim 1, wherein in the step 3), the optical property constants of the supercell model of the surface of ZnO (0001) by doping and adsorbing Fe atoms are obtained by the following method:
a. the study of the optical properties of materials using the first principle of linearity is guided by the dielectric function, in the linear response range, the macroscopic optical response function of a solid is described by the complex dielectric constant (ω) of light:
(ω)＝1(ω)+i2(ω) (2)
wherein: omega is the frequency of the wave to be measured,1(ω) and2(ω) is the real and imaginary parts of the dielectric function, respectively;
b. imaginary part of dielectric function in the above equation2(ω) is calculated from the matrix elements between the electron wave functions of the occupied and unoccupied states:
Figure FDA0002493886800000032
wherein: omega is the unit cell volume, is the dirac function,0the dielectric constant in vacuum, c and v are the conduction band and the valence band, respectively, k is the reciprocal lattice vector,
Figure FDA0002493886800000033
and
Figure FDA0002493886800000034
intrinsic energy levels in the conduction and valence bands, respectively, u is the vector defining the polarization of the incident electric field, r is the position vector,
Figure FDA0002493886800000041
and
Figure FDA0002493886800000042
wave functions of conduction band and valence band, respectively;
and real part1(ω) from the imaginary part using the Kramers-Kronig relationship2(ω) is calculated as:
Figure FDA0002493886800000043
wherein: p is the principal value of the integral;
c. the optical property constants of the material are all composed of1(ω) and2(ω) is derived as:
absorption coefficient α (ω):
Figure FDA0002493886800000044
reflectance R (ω):
Figure FDA0002493886800000045
refractive index n (ω):
Figure FDA0002493886800000046
energy loss spectrum L (ω):
Figure FDA0002493886800000047
6. the calculation method for improving photocatalytic property of ZnO (0001) surface by doping and adsorbing Fe atoms according to claim 1, wherein in the step 3), the work function W of the ZnO (0001) surface adsorbed by Fe atoms isfThe solution is made according to the following formula:
Wf＝Evac-EF(9)
in the formula, EvacIs a vacuum level, EFIs the fermi level.
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