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Issue 6, 2010
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Three- and four-body nonadditivities in nucleic acid tetramers: a CCSD(T) study

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Abstract

Three- and four-body nonadditivities in the uracil tetramer (in DNA-like geometry) and the GC step (in crystal geometry) were investigated at various levels of the wave-function theory: HF, MP2, MP3, L-CCD, CCSD and CCSD(T). All of the calculations were performed using the 6-31G**(0.25,0.15) basis set, whereas the HF, MP2 and the MP3 nonadditivities were, for the sake of comparison, also determined with the much larger aug-cc-pVDZ basis set. The HF and MP2 levels do not provide reliable values for many-body terms, making it necessary to go beyond the MP2 level. The benchmark CCSD(T) three- and four-body nonadditivities are reasonably well reproduced at the MP3 level, and almost quantitative agreement is obtained (fortuitously) either on the L-CCD level or as an average of the MP3 and the CCSD results. Reliable values of many-body terms (especially their higher-order correlation contributions) are obtained already when the rather small 6-31G**(0.25,0.15) basis set is used. The four-body term is much smaller when compared to the three-body terms, but it is definitely not negligible, e.g. in the case of the GC step it represents about 16% of all of the three- and four-body terms. While investigating the geometry dependence of many-body terms for the GG step at the MP3/6-31G**(0.25,0.15) level, we found that it is necessary to include at least three-body terms in the determination of optimal geometry parameters.

Graphical abstract: Three- and four-body nonadditivities in nucleic acid tetramers: a CCSD(T) study

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Article information


Submitted
17 Sep 2009
Accepted
18 Nov 2009
First published
18 Dec 2009

Phys. Chem. Chem. Phys., 2010,12, 1369-1378
Article type
Paper

Three- and four-body nonadditivities in nucleic acid tetramers: a CCSD(T) study

M. Pitoňák, P. Neogrády and P. Hobza, Phys. Chem. Chem. Phys., 2010, 12, 1369
DOI: 10.1039/B919354E

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