6533b7d9fe1ef96bd126cc3c

RESEARCH PRODUCT

Perturbative treatment of the electron-correlation contribution to the diagonal Born-Oppenheimer correction.

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A perturbative scheme for the treatment of electron-correlation effects on the diagonal Born-Oppenheimer correction (DBOC) is suggested. Utilizing the usual Moller-Plesset partitioning of the Hamiltonian formulas for first and second orders (termed as MP1 and MP2) are obtained by expanding the wave function in the corresponding coupled-cluster expressions for the DBOC[J. Gauss et al., J. Chem. Phys. 125, 144111 (2006)]. The obtained expressions are recast in terms of one- and two-particle density matrices in order to take advantage of existing analytic second-derivative implementations for many-body methods. Test calculations show that both MP1 and MP2 recover large fractions (on average 90% and 95%, respectively) of the coupled-cluster singles and doubles (CCSD) electron-correlation corrections to the DBOC and thus render the suggested MP treatments cost-effective (though still accurate) alternatives to high-level coupled cluster (CC) treatments. The applicability of the MP1 and MP2 schemes for treating DBOC is demonstrated in calculations for the atomization energies of benzene, naphthalene, anthracene, and tetracene. The corresponding corrections are surprisingly large (about 0.6 kJmol for benzene, 1.1 kJmol for naphthalene, 1.5 kJmol for anthracene, and 1.8 kJmol for tetracene) with the electron-correlation corrections reducing the corresponding Hartree-Fock self-consistent field values by 25%-30%.