doi:10.1016/S0166-1280(00)00496-6 
Copyright © 2000 Elsevier Science B.V. All rights reserved.
Time-dependent density-functional theory investigation of excitation spectra of open-shell molecules*1, , *2
J. Guan, M. E. Casida
, 
and D. R. Salahub
Département de chimie, Université de Montréal C.P. 6128, Succursale centre-ville, Montréal, Quebec, Canada H3C 3J7
Received 25 January 2000;
revised 16 February 2000;
accepted 24 February 2000.
Available online 3 August 2000.
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Abstract
Time-dependent density-functional theory is developed for open-shell molecular systems and implemented in the post-deMon program, DynaRho (version 2pX). In case studies, this time-dependent density-functional theory is applied to study excitation energies and oscillator strengths of open-shell molecules, three neutral molecules (BeH, BeF, CN) and three positive ions (CO+, N2+, CH2O+). To our knowledge, our calculated excitation spectra of such open-shell molecules are the first applications of time-dependent density-functional theory to such open-shell systems, except for the recent calculation of the lowest two excitation energies (without oscillator strengths) of a few open-shell molecules [S. Hirata, M. Head-Gordon, Chem. Phys. Lett. 302 (1999) 375] and the calculation of the potential energy surfaces of excited states of the open-shell species PO [A. Spielfiedel, N.C. Handy, Phys. Chem. Chem. Phys. 1 (1999) 2401]. The present calculations of the open-shell molecules show that time-dependent density-functional theory can treat open-shell systems fairly well, and the present calculated excitation energies with both LSDxc/TDLSDxc and LB94xc/TDLSDxc functionals are comparable with traditional ab initio methods.
Author Keywords: Time-dependent density-functional theory; Excitation spectra; Open-shell molecules
Fig. 1. Excitation spectrum of BeH with the LSDxc/TDLSDxc functional and the Sadlej basis.
Fig. 2. Excitation spectrum of BeH with the LB94xc/TDLSDxc functional and the Sadlej basis.
Fig. 3. Excitation spectrum of BeF with the LSDxc/TDLSDxc functional and the Sadlej basis.
Fig. 4. Excitation spectrum of BeF with the LB94xc/TDLSDxc functional and the Sadlej basis.
Fig. 5. Excitation spectrum of CN with the LSDxc/TDLSDxc functional and the extended Sadlej basis.
Fig. 6. Excitation spectrum of CN with the LSDxc/TDLSDxc functional and the Sadlej basis.
Fig. 7. Excitation spectrum of CN with the LB94xc/TDLSDxc functional and the Sadlej basis.
Fig. 8. Excitation spectrum of CO+ with the LSDxc/TDLSDxc functional and the Sadlej basis.
Fig. 9. Excitation spectrum of CO+ with the LB94xc/TDLSDxc functional and the Sadlej basis.
Fig. 10. Excitation spectrum of N2+ with the LSDxc/TDLSDxc functional and the Sadlej basis.
Fig. 11. Excitation spectrum of N2+ with the LB94xc/TDLSDxc functional and the Sadlej basis.
Fig. 12. Excitation spectrum of CH2O+ with the LSDxc/TDLSDxc functional and the Sadlej basis.
Fig. 13. Excitation spectrum of CH2O+ with the LB94xc/TDLSDxc functional and the Sadlej basis.
Fig. 14. Excitation spectrum of CH2O+ with the MRD-CI method taken from [105].
Fig. 15. Potential energy curves of CH2O+ for low lying doublet states with the LSDxc/TDLSDxc functional and the Sadlej basis.
Fig. 16. Potential energy curves of CH2O+ for low lying doublet states calculated by the MRD-CI, reproduced with permission from Taylor and Francis, from [105].
Table 1. Experimental geometries (taken from [82]) of the six chosen small molecules used in present calculations
Table 4. BeF vertical excitation energies (eV) calculated with the LSDxc/TDLSDxc and the LB94xc/TDLSDxc functionals using the Sadlej basis set ((52111/411/22) for fluorine taken from [106] and (52111/411/22) for beryllium, taken from [98])
Table 5. CN vertical excitation energies (eV) calculated with the LSDxc/TDLSDxc and the LB94xc/TDLSDxc functionals using the Sadlej basis set ((52111/411/22) for carbon and nitrogen taken from [106])
Table 7. N2+ vertical excitation energies (eV) calculated with the LSDxc/TDLSDxc and the LB94xc/TDLSDxc functionals and with the cation and the neutral N2 molecular geometries using Sadlej basis set ((52111/411/22) for nitrogen taken from [106])
Table 2. Ground state configurations for the six chosen molecules from the present DFT SCF calculations
Table 3. BeH vertical excitation energies (eV) calculated with the LSDxc/TDLSDxc and the LB94xc/TDLSDxc functionals using the Sadlej basis set ((411/22) for hydrogen taken from [106] and (52111/411/22) for beryllium, taken from [98])
Table 6. Carbon monoxide positive ion vertical excitation energies (eV) calculated with the LSDxc/TDLSDxc and the LB94xc/TDLSDxc functionals and with the cation and the neutral CO molecular geometries using Sadlej basis set ((52111/411/22) for carbon and oxygen taken from [98])
Table 8. CH2O+ vertical excitation energies (eV) calculated with the LSDxc/TDLSDxc and the LB94xc/TDLSDxc functionals using the Sadlej basis set ((411/22) for hydrogen taken from [106] and (52111/411/22) for carbon and oxygen taken from [98]) and the extended Sadlej basis (XB) (extended Sadlej basis is (41111/221) for hydrogen, (5211111/4111/221) for carbon and oxygen, see text)
Table 9. Comparison of experimental ionization potential and −εHOMO of small molecules calculated with LSDxc and LB94xc functionals
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