Gaussian-3 theory using density functional geometries and zero-point energies
- Chemistry and Materials Science Divisions, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
- Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974 (United States)
A variation of Gaussian-3 (G3) theory is presented in which the geometries and zero-point energies are obtained from B3LYP density functional theory [B3LYP/6-31G(d)] instead of geometries from second-order perturbation theory [MP2(FU)/6-31G(d)] and zero-point energies from Hartree{endash}Fock theory [HF/6-31G(d)]. This variation, referred to as G3//B3LYP, is assessed on 299 energies (enthalpies of formation, ionization potentials, electron affinities, proton affinities) from the G2/97 test set [J. Chem. Phys. {bold 109}, 42 (1998)]. The G3//B3LYP average absolute deviation from experiment for the 299 energies is 0.99 kcal/mol compared to 1.01 kcal/mol for G3 theory. Generally, the results from the two methods are similar, with some exceptions. G3//B3LYP theory gives significantly improved results for several cases for which MP2 theory is deficient for optimized geometries, such as CN and O{sub 2}{sup +}. However, G3//B3LYP does poorly for ionization potentials that involve a Jahn{endash}Teller distortion in the cation (CH{sub 4}{sup +}, BF{sub 3}{sup +}, BCl{sub 3}{sup +}) because of the B3LYP/6-31G(d) geometries. The G3(MP2) method is also modified to use B3LYP/6-31G(d) geometries and zero-point energies. This variation, referred to as G3(MP2)//B3LYP, has an average absolute deviation of 1.25 kcal/mol compared to 1.30 kcal/mol for G3(MP2) theory. Thus, use of density functional geometries and zero-point energies in G3 and G3(MP2) theories is a useful alternative to MP2 geometries and HF zero-point energies. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 336655
- Journal Information:
- Journal of Chemical Physics, Vol. 110, Issue 16; Other Information: PBD: Apr 1999
- Country of Publication:
- United States
- Language:
- English
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