| Study of the electron excited state of molecules is of great significance to the development of modern physics and chemistry,such as understanding the mechanism of optoelectronic functional materials,resolving absorption and emission spectra of molecules and simulating photophysical and photochemical processes.At present,whether based on the density functional theory method or many methods based on the wave function theory,the study of the electron excited state of the small molecule and the closed shell system has good results.However,for the large moelcular systems,TD-DFT is the only way to calculate the excited state of electrons due to computational limitations.But for the open shell system,the unrestricted TD-DFT underestimates the excitation energy of some states due to the spin contamination.Aiming at this problem,Li Zhendong and Liu Wenjian proposed a spin-adapted TD-DFT(X-TD-DFT)theory based on tensor coupling.X-TD-DFT successfully solved the spin contamination problem of open shell system,and was verified in many main group free radical systems.But whether this method is applicable for transition metal systems,which have more complex electronic structures is rarely reported.For this reason,seven transition metal compounds:ZnH,CdH,ScH2,YH2,ScO,YO,NbO2 were selected according to the complexity of electrrnoic structure.The electron excited state was calculated by X/U-TD-DFT with different functionalities compared to multi-reference method MS-CASPT2 and ic-MRCISD.The result shows:(1)For hydride ZnH,CdH,ScH2,YH2,X-TD-DFT corrects the U-TD-DFT which underestimates the excitation energy due to spin contamination.For ZnH and CdH,some excited states belong to the Rydberg state and the LC-BLYP functional gives the best results.For ScH2 and YH2,some excited states belong to charge transfer state and BHandHLYP and CAM-B3LYP functional gives the best results.(2)For oxides ScO,YO and NbO2,U-TD-DFT overestimate energy of som excitation state because of the double excitation which is opposite to the result of spin contamination excitation state.For example,for SAOP,PBEO,BHandHLYP,LC-BLYP and CAM-B3LYP functional,the error statistic of U-TD-DFT is less than X-TD-DFT.Finally,the spectral parameters of[Cu(C6H6)2]2+ were calculated by X/U-TD-DFT,respectively.The results show that X-TD-DFT corrects the U-TD-DFT due to spin contamination,and obtains a new result which is more consistent with the experimental results. |
