S. Kawahara et al., Electron correlation and basis set effects on strong hydrogen bond behavior: a case study of the hydrogen difluoride anion, CHEM PHYS, 273(2-3), 2001, pp. 207-216
A strong hydrogen bond between hydrogen fluoride and fluoride anions forms
an anionic chemical species., i.e. a hydrogen difluoride anion. This paper
describes the result of ab initio investigations on hydrogen bond behavior
of the hydrogen difluoride anion, whose geometry and energy were evaluated
at various computational levels of theory, from Hartree-Fock to QCISD(T) ca
lculations using basis sets from cc-pVDZ to aug-cc-pV5Z. The MP4(SDQ) or QC
ISD level of calculations using aug-cc-pVTZ or a larger basis set suggested
an almost constant value (2.27 Angstrom) for the atom distance between two
fluorine atoms. The larger basis set was utilized, the more negative (the
larger) hydrogen bond energy was suggested. But when aug-cc-pVTZ or a large
r basis set was utilized, the fluctuation of the calculated values for hydr
ogen bond energy was less than I kcal/mol. Accurate estimation of the hydro
gen bond energy requires MP4(SDQ) geometry optimization and subsequent QCIS
D(T) energy estimation. But the difference in the geometry and energy betwe
en the MP2 and QCISD results was small and, thus, the MP2 results are consi
dered reliable despite the low computational costs. The change in the poten
tial energy was also examined for dissociation of the hydrogen difluoride a
nion into hydrogen fluoride and fluoride anions. The potential energy curve
obtained from the computational level of QCISD(T)/aug-cc-pVTZ//MP4(SDQ)/au
g-cc-pVTZ was in good agreement with that obtained from the calculation of
QCISD(T)/aug-cc-pV5Z//MP4(SDQ)/aug-cc-pVTZ. (C) 2001 Elsevier Science BN. A
ll rights reserved.