The accuracy of local MP2 methods for conformational energies

Jakub Kaminsky (1) , Ricardo André Fernandes Mata (2) , Hans-Joachim Werner (3) , Frank Jensen (4)

1 IOCB / CAS - Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences
2 Institut für Theoretische Chemie [Stuttgart]
3 Institute for Theoretical Chemistry
4 Department of Chemistry

The relative energies of 95 conformers of four peptide models are studied using MP2 and LMP2 methods and correlation consistent basis sets ranging from double-zeta to augmented quintuplezeta quality. It is found that both methods yield quite similar results, and the differences between MP2 and LMP2 decrease systematically with increasing basis set. Due to reduced intramolecular basis set superposition effects (BSSE) the LMP2 results converge more slowly to basis set limit for most of these rather small systems. However, for larger peptides, the BSSE has a very large effect on the energy difference between extended and helical structures, leading to a very strong basis set dependence of the canonical MP2 results. It is demonstrated for alanine octapeptides that the basis set error exceeds 30 and 20 kJ/mol, respectively, if augmented double-zeta and triple-zeta basis sets are used. On the other hand, the LMP2 results are only slightly affected by the basis set size, and even with augmented double-zeta basis sets reasonably accurate results are obtained. Furthermore, for the larger systems the computation times for the LMP2 calculations are shown to be up to one order or magnitude shorter than for canonical MP2 calculations with the same basis set.

Mots clés: Physical Sciences

Jakub Kaminsky, Ricardo André Fernandes Mata, Hans-Joachim Werner, Frank Jensen. The accuracy of local MP2 methods for conformational energies. Molecular Physics, 2008, 106 (15), pp.1899-1906. ⟨10.1080/00268970802360355⟩. ⟨hal-00513225⟩