Jakubowska K, Pecul M, Ruud K. Relativistic Four-Component DFT Calculations of Vibrational Frequencies.
J Phys Chem A 2021;
125:10315-10320. [PMID:
34843253 PMCID:
PMC8667032 DOI:
10.1021/acs.jpca.1c07398]
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Abstract
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We investigate the
effect of relativity on harmonic vibrational
frequencies. Density functional theory (DFT) calculations using the
four-component Dirac–Coulomb Hamiltonian have been performed
for 15 hydrides (H2X, X = O, S, Se, Te, Po; XH3, X = N, P, As, Sb, Bi; and XH4, X = C, Si, Ge, Sn, Pb)
as well as for HC≡CPbH3. The vibrational frequencies
have been calculated using finite differences of the molecular energy
with respect to geometrical distortions of the nuclei. The influences
of the choice of basis set, exchange–correlation functional,
and step length for the numerical differentiation on the calculated
harmonic vibrational frequencies have been tested, and the method
has been found to be numerically robust. Relativistic effects are
noticeable for the heavier congeners H2Te and H2Po, SbH3 and BiH3, and SnH4 and
PbH4 and are much more pronounced for the vibrational modes
with higher frequencies. Spin–orbit effects constitute a very
small fraction of the total relativistic effects, except for H2Te and H2Po. For HC≡CPbH3 we
find that only the frequencies of the modes with large contributions
from Pb displacements are significantly affected by relativity.
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