ISSN:
0040-5744
Keywords:
Key words: BeO molecule
;
Coupled-cluster calculations
;
Quadratic configuration interaction
;
Spectroscopy
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Summary. This paper reports a series of coupled-cluster (CC) calculations through CCSDT on the theoretically challenging ground state of the BeO molecule. Along with CC methods, quadratic configuration interaction (QCI) approximations to CC theory have been used (QCISD and QCISD(T)), which show several dramatic failings. Equilibrium electrical properties (μ, α xx , and α zz ) and basic spectroscopic properties (r e, ωe, D e, and infrared intensity (I)) have been computed. Basis set and electron correlation effects are analyzed in order to arrive at accurate values of the dipole moment and polarizability, which are not known experimentally. For the dipole moment, we obtain a value of 6.25 D, with an uncertainty of about 0.1 D. For α xx and α zz , we suggest respective values of 32 and 36 atomic units (a.u.) and error bars of about 1 and 2 a.u. With extended basis sets, the spectroscopic properties r e, ωe, and D e are reproduced to high accuracy, which is the first time this has been achieved for this species by ab initio methods. At the highest calculation levels, I is predicted to be very small. Although I has not been measured, some support for this prediction comes from a recent infrared study of BeO–rare gas complexes. The QCI methods are shown to be much more sensitive to basis set, and even with large basis sets yield values of α zz and I which differ from CC results by an order of magnitude and three orders of magnitude, respectively. These differences doubtless arise from the importance of single excitations (T 1) for this molecule, as several terms involving T 1 are neglected in the QCISD approximation compared with CCSD. We also report CC calculations with Brueckner orbitals, which yield results similar to those obtained with restricted Hartree–Fock orbitals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01113541
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