EXCITATION-ENERGIES, OSCILLATOR-STRENGTHS, AND FREQUENCY-DEPENDENT POLARIZABILITIES OF BE - COMPARISON OF TDHF, EOM (2ND-ORDER), AND MCTDHF
Academic Article
Overview
Identity
Additional Document Info
Other
View All
Overview
abstract
Lowlying excitation energies from the ground state of Be were calculated using a basis set of 61 Cartesian Gaussian functions. Three approximations were employed: the timedependent HartreeFock (TDHF), secondorder equationsofmotion (EOM), and multiconfigurational timedependent HartreeFock (MCTDHF). The TDHF excitation energies are 0.51.1 eV lower than experiment, and the EOM values are 0.31.2 eV lower than experiment, whereas the MCTDHF excitation energies deviate on the absolute average from experiment by only 0.03 eV. We found that in an MCTDHF calculation, any proper MCSCF stationary point is a good reference (i.e., initial) state, not just the ground state. Experimental values for oscillator strength are accurately known only for the 2s2X1S 2s2p1P0 transition. The TDHF value and the MCTDHF value agree with experiment, but the EOM value does not. The agreement of the TDHF value with experiment seems to be coincidental, because for higher lying transitions the TDHF values differ by approximately a factor of two or more from the more accurate MCTDHF. Frequency independent polarizabilities, (0), were also calculated with the TDHF, HRPA, and MCTDHF and frequency dependent polarizabilities, (), were calculated with the MCTDHF. No experimental data for Be polarizabilities exist, but we expect the MCTDHF values to be among the most accurate calculations available. Copyright 1987 John Wiley & Sons, Inc.
