Transition states for hydrogen radical reactions: LiFH as a stringent test case for density functional methods

Author: Ventura O. N.

Source: Molecular Physics, Volume 89, Number 6, 20 December 1996 , pp. 1851-1870(20)

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Abstract:

The Becke three-parameter Lee-Yang-Parr (B3LYP) density functional method is applied to the study of the reaction Li + HF H + LiF; the results obtained are compared with experiment and previous multireference singles and doubles configuration interaction (MRDCI) calculations, and with singles and doubles quadratic configuration interaction (QCISD) and Gaussian 2 (G2) model chemistry calculations performed also in this paper. It is found that, using an extended 6-311 + G(3df,3pd) basis set, the predicted stabilization enthalpy of the initial LiFH complex (- 34.6 kJ mol-1) and the exoergicity of the reaction (-7.3 kJ mol-1) are predicted in agreement with experiment (~ - 31 kJ mol-1 and - 4.8 +/- 8 kJ mol-1, respectively). These results are also in agreement with the MRDCI calculations (~ - 31.5 kJ mol-1 and - 9 kJ mol-1, respectively). However, the energy of the transition state with respect to the reactants at the B3LYP level is about 25 kJ mol-1 lower than the MRDCI result (which agrees with the QCISD and G2 values). Therefore, it is concluded that B3LYP is not describing this reaction properly. It is shown, however, that this defect is due mainly to the inclusion of the LYP correlation functional instead of the Perdew-Wang originally considered by Becke for developing his adiabatically connected functional. When B3PW91 is considered instead of B3LYP, the height of the transition state is in better agreement with the conventional ab initio methods, although still off by 50%.

Language: English

Document Type: Research article

Publication date: 1996-12-20

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