The Electronic Structure and Vibrational Spectrum of trans-HNOO
Department of Chemistry and Biochemistry, Calvin College, Grand Rapids, Michigan, United StatesThe Journal of Physical Chemistry A (Impact Factor: 2.69). 04/2004; 108(15):2893-2903. DOI: 10.1021/jp036809q
This paper reports the theoretical results of a thorough, state-of-the-art, coupled-cluster, renormalized coupled-cluster, and vibrational study on the molecule imine peroxide, HNOO, in its trans conformation. This molecule is isoelectronic with ozone and presents many of the same difficulties for theory as ozone. We report both the theoretical geometry and the vibrational frequencies, including anharmonic corrections to the computed harmonic vibrational frequencies obtained by calculating the quartic force field at the high levels of coupled cluster theory, including CCSD(T) and its renormalized and completely renormalized extensions and methods including the combined effect of triply and quadruply excited clusters [CCSD(TQ f) and CCSDT-3(Q f)]. The motivation behind our study was the disagreement between two previous reports that appeared in the literature on HNOO, both reporting theoretical (harmonic) and experimental (matrix isolation) vibrational spectra of HNOO. Our new theoretical results and our analysis of the previous two papers strongly suggest that the correct assignment of vibrational spectra is that of Laursen, Grace, DeKock, and Spronk (J. Am. Chem. Soc. 1998, 120, 12583-12594). We also compare the electronic structure of HNOO with the isoelectronic molecules HONO and O 3 . The NO and OO bond lengths are practically identical in HNOO, in agreement with the identical OO bond lengths (by symmetry) in ozone. Correspondingly, the NO and OO stretching frequencies of trans-HNOO are in close proximity to each other, as are the symmetric and antisymmetric OO stretching frequencies in O 3 . This is in contrast to the electronic structure of HONO, which has a large difference between the two NO bond lengths, and a correspondingly large difference between the two NO vibrational frequencies. These results are readily understood in terms of simple Lewis electron dot structures.
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ABSTRACT: Two new classes of non-iterative corrections to the ground- and excited-state energies obtained in the state-universal multi-reference coupled-cluster (SUMRCC) calculations have been developed using the multi-reference extension of the method of moments of coupled-cluster equations (MMCC) [KOWALSKI, K., and PIECUCH, P., 2001, J. molec. Struct. (THEOCHEM), 547, 191]. In the first class of the configuration interaction (CI) corrected multi-reference MMCC (MRMMCC) approximations, the non-iterative corrections due to triply or triply and quadruply excited clusters are constructed with the help of multi-reference CI (MRCI) calculations employing the same active space as used in the SUMRCC calculations. In the second class of the completely renormalized (CR) SUMRCC methods, which can be viewed as the multi-reference extensions of the single-reference CR-CCSD(T) theory [KOWALSKI, K., and PIECUCH, P., 2000, J. chem. Phys., 113, 18], the non-iterative corrections due to triply excited clusters are constructed with the help of the multi-reference many-body perturbation theory. In both cases, the non-iterative corrections due to higher-order clusters are added to the energies obtained with the SUMRCC method with singles and doubles. It is demonstrated that the newly developed corrections, including the CR-SUMRCC methods, offer considerable improvements in the SUMRCCSD results, reducing, in particular, the large errors in the SUMRCCSD results due to intruders.Molecular Physics 12/2004; 102(23-24):2425-2449. DOI:10.1080/00268970412331292867 · 1.72 Impact Factor
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ABSTRACT: It is shown that the extended coupled-cluster method with singles and doubles (ECCSD) does not suffer from the non-variational collapse observed in the standard CCSD calculations when multiple bond breaking is examined. This interesting feature of the single-reference ECCSD theory is used to design the non-iterative CC methods with singles, doubles and non-iterative triples and quadruples, which provide a highly accurate and variational description of potential energy surfaces involving multiple bond breaking with computational steps that scale as with the system size. This is accomplished with the help of the generalized version of the method of moments of coupled-cluster equations (GMMCC), which can be used to correct the results of non-standard CC calculations, such as ECCSD. The theoretical considerations are illustrated by the preliminary results of the ECCSD-based GMMCC calculations for triple bond breaking in N2.Molecular Physics 08/2005; 103(15-16):2191-2213. DOI:10.1080/00268970500131595 · 1.72 Impact Factor
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ABSTRACT: For the first time high-order excitations (n>2) have been studied in three multireference couple cluster (MRCC) theories built on the wave operator formalism: (1) the state-universal (SU) method of Jeziorski and Monkhorst (JM) (2) the state-specific Brillouin-Wigner (BW) coupled cluster method, and (3) the state-specific MRCC approach of Mukherjee (Mk). For the H4, P4, BeH(2), and H8 models, multireference coupled cluster wave functions, with complete excitations ranging from doubles to hextuples, have been computed with a new arbitrary-order string-based code. Comparison is then made to corresponding single-reference coupled cluster and full configuration interaction (FCI) results. For the ground states the BW and Mk methods are found, in general, to provide more accurate results than the SU approach at all levels of truncation of the cluster operator. The inclusion of connected triple excitations reduces the nonparallelism error in singles and doubles MRCC energies by a factor of 2-10. In the BeH(2) and H8 models, the inclusion of all quadruple excitations yields absolute energies within 1 kcal mol(-1) of the FCI limit. While the MRCC methods are very effective in multireference regions of the potential energy surfaces, they are outperformed by single-reference CC when one electronic configuration dominates.The Journal of Chemical Physics 10/2006; 125(15):154113. DOI:10.1063/1.2357923 · 2.95 Impact Factor
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