Timedependent density functional study of the electronic potential energy curves and excitation spectrum of the oxygen molecule
Article
English
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Guan, Jingang
;
Wang, Fan
;
Ziegler, Tom
;
Cox, Hazel
(2006)
Orbital energies, ionization potentials, molecular constants, potential energy curves, and the excitation spectrum of O(2) are calculated using timedependent density functional theory (TDDFT) with TammDancoff approximation (TDA). The calculated negative highest occupied molecular orbital energy (epsilon(HOMO)) is compared with the energy difference ionization potential for five exchange correlation functionals consisting of the local density approximation (LDAxc), gradient corrected Becke exchange plus Perdew correlation (B(88X)+P(86C)), gradient regulated asymptotic correction (GRAC), statistical average of orbital potentials (SAOP), and van Leeuwen and Baerends asymptotically correct potential (LB94). The potential energy curves calculated using TDDFT with the TDA at internuclear distances from 1.0 to 1.8 A are divided into three groups according to the electron configurations. The 1pi(u) (4)1pi(g) (2) electron configuration gives rise to the X (3)Sigma(g) (), a (1)Delta(g), and b (1)Sigma(g) (+) states; the 1pi(u) (3)1pi(g) (3) electron configuration gives rise to the c (1)Sigma(u) (), C (3)Delta(u), and A (3)Sigma(u) (+) states; and the B (3)Sigma(u) (), A (1)Delta(u), and f (1)Sigma(u) (+) states are determined by the mixing of two or more electron configurations. The excitation spectrum of the oxygen molecule, calculated with the aforementioned exchange correlation functionals, shows that the results are quite sensitive to the choice of functional. The LDAxc and the B(88X)+P(86C) functionals produce similar spectroscopic patterns with a single strongly absorbing band positioned at 19.82 and 19.72 eV, respectively, while the asymptotically corrected exchange correlation functionals of the SAOP and the LB94 varieties yield similar excitation spectra where the computed strongly absorbing band is located at 16.09 and 16.42 eV, respectively. However, all of the exchange correlation functionals yield only one strongly absorbing band (oscillator strength greater than 0.1) in the energy interval of 020 eV, which is assigned to a X (3)Sigma(g) () to (3)Sigma(u) () transition. Furthermore, the oxygen molecule has a rich spectrum in the energy range of 1420 eV and no spin allowed absorption bands are predicted to be observed in the range of 06 eV.

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