Raman Spectra Of Vanadium Pentoxide From First-Principles Calculation

With the progress in density functional theory(DFT) and its numerical methods, DFT based first-principles calculation has become a routine method for condensed matter theory,quantum chemistry and material science.The plane-wave pseudopotential method and the local-density approximation(LDA) to density-functional theory(DFT) have provided a simple framework whose accuracy and predictive power have been convincingly demonstrated in a large variety of systems.Recently,very efficient linear-response techniques have been proposed which allow one to obtain dynamical matrices at arbitrary wave vectors with computational effort comparable to the self-consistent calculation for the unperturbed bulk.It is by now possible to obtain accurate phonon dispersions on a fine grid of wave vectors covering the entire Brillouin zone(BZ),which can compare directly with neutron-diffraction data.The Raman spectra and infrared spectra obtained from linear response method are helpful for experiments.Vanadium is a typical transition metal element with much active chemical properties.It can form many kinds of oxides,among which,vanadium pentoxides attract most of focus from experimental and theoretical study because of its special and variant structures.The main progresses of this work are lists as follows:First,we summarize the process of calculating Raman sepctrac from first principles method,which is besed on density functional perturbation theory.The density functional perturbation theory is built on the framework of density function. We give a detailed description of this method,from a programmer aspect.We also state out the process of how to use ABINIT software package to calculate the Raman spectra of cystals.Second,the band structure ofα-,β-,γ-V₂O₅ have been obtained.The band gap ofα-V₂O₅ is 2.30 eV,which is the same as measured from experiments.The band gap ofβ-V₂O₅ is 1.66 eV.Compared from band structure,β-V₂O₅ has the highest electronic mobility than others.We also study the relation of band structure and the crystal structureThird,we obtained the Raman sepctrum ofα-,β-V₂O₅,using DFPT method.The calculated spectra fit the experiments very well.And we first present the phonon dispersion ofα-,β-V₂O₅.These data are valuable for interepting the experimental Raman sepctrum of vanadium oxide compounds.Then we fully study the transient process fromα- toβ-V₂O₅.