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Ab initio calculations of weakly bonded He 2 and Be 2 molecules by MRCI method with pseudo‐natural molecular orbitals
Author(s) -
Mitin Alexander V.
Publication year - 2011
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.22691
Subject(s) - chemistry , van der waals force , ab initio , gaussian , atomic orbital , wave function , natural bond orbital , bond dissociation energy , atomic physics , molecule , molecular orbital , bond length , dissociation (chemistry) , computational chemistry , physics , quantum mechanics , density functional theory , electron , organic chemistry
The X 1 Σ g +curves of He 2 and Be 2 have been calculated by extrapolating the BSSE corrected MRCI total energies obtained with large Gaussian basis sets, large reference configuration spaces, and pseudo‐natural molecular orbitals to an infinite basis. The direct calculated He 2 nonrelativistic dissociation energies ( D e ) of 11.0031 K is in excellent agreement with the recent theoretical evaluations, whereas the Be 2 nonrelativistic D e = 822 cm −1 and relativistically corrected D e = 818 cm −1 are in good agreement with most known values including the experimental D e = 790 ± 30 cm −1 . An analysis of the configuration structure of Be 2 wave function and calculated vibration spectrum displays unusual type of chemical bond in this molecule and explains a unique form of the Be 2 potential curve. Thus, near the equilibrium point the bond can be classified as a conventional covalent bond, whereas at larger distances, it can be classified as van der Waals interaction. The problems of high precision Be 2 potential curve calculations are also discussed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011