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Coupled cluster and configuration interaction quantum calculations of infrared fundamental intensities
Author(s) -
da Silva João Viçozo,
Vidal Luciano N.,
Vazquez Pedro A. M.,
Bruns Roy E.
Publication year - 2010
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.22707
Subject(s) - basis set , coupled cluster , chemistry , perturbation theory (quantum mechanics) , atomic physics , basis (linear algebra) , electronic correlation , atomic orbital , cluster (spacecraft) , molecular physics , physics , computational chemistry , electron , quantum mechanics , molecule , mathematics , density functional theory , geometry , organic chemistry , computer science , programming language
The fundamental infrared intensities of HF, H 2 O, HCN, CH 3 F, CH 4 , C 2 H 6 , C 2 H 2 , and C 2 H 4 have been calculated at the quadratic configuration interaction and coupled cluster levels using a wide variety of basis sets. Both these levels contemplated single and double excitations and most of the coupled cluster calculations included triple excitations. The basis sets used included the cc‐pVXZ (X = D,T,Q,5) sets, with and without polarization orbitals, the aug‐cc‐pVTZ set, and the Sadlej Z2PolX, Z3PolX, and pVTZ basis sets The theoretical results depended more on basis set variation rather than changes between the CCSD(T) and QCISD levels, although the results from these electron correlation treatment levels are quite different from those obtained at the second‐order Moller‐Plesset perturbation level. Principal component and hierarchical clustering analyses confirm the stronger basis set dependence of the intensity values. The cc‐pVTZ basis set gives results that are about twice as accurate as those obtained using the smaller cc‐pVDZ. However, basis sets that are larger than cc‐pVTZ are not seen to improve accuracy. Most accurate intensity results were obtained using the CCSD(T)/cc‐pVTZ and QCISD/cc‐pVTZ levels with root mean square (rms) errors of 5.4 and 5.9 km mol −1 . This compares with a rms error of 11.7 km mol −1 for results obtained at the MP2/6‐311++G(3d,3p) level that has often been used to calculate infrared fundamental intensities. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010