Electronic States Of Methylene Research Articles

Comparison of the completely renormalized equation-of-motion coupled-cluster and Quantum Monte Carlo results for the low-lying electronic states of methylene

The left-eigenstate completely renormalized (CR) equation-of-motion (EOM) coupled-cluster (CC) method with singles, doubles, and non-iterative triples, abbreviated as CR-EOMCC(2,3) [M. Włoch et al., Mol. Phys. 104, 2149 (2006); P. Piecuch et al., Int. J. Quantum Chem. 109, 3268 (2009)], and the companion ground-state CR-CC(2,3) methodology [P. Piecuch and M. Włoch, J. Chem. Phys. 123, 224105 (2005); P. Piecuch et al., Chem. Phys. Lett. 418, 467 (2006)] are used to determine the total electronic and adiabatic excitation energies corresponding to the ground and lowest three excited states of methylene. The emphasis is on comparing the CR-CC(2,3)/CR-EOMCC(2,3) results obtained with the large correlation-consistent basis sets of the aug-cc-pCV xZ (x = T, Q, 5) quality and the corresponding complete basis set (CBS) limits with the recently published variational and diffusion Quantum Monte Carlo (QMC) data [P. Zimmerman et al., J. Chem. Phys. 131, 124103 (2009)]. It is demonstrated that the CBS CR-CC(2,3)/CR-EOMCC(2,3) results are in very good agreement with the best QMC, i.e. diffusion MC (DMC) data, with errors in the total and adiabatic excitation energies of all calculated states on the order of a few millihartree and less than 0.1 eV, respectively, even for the challenging, strongly multi-reference C 1 A 1 state for which the basic EOMCC approach with singles and doubles completely fails. The agreement between the CBS CR-CC(2,3)/CR-EOMCC(2,3) and variational MC (VMC) results for the total energies is not as good as in the DMC case, but the excitation energies resulting from the CBS CR-CC(2,3)/CR-EOMCC(2,3) and VMC calculations agree very well.

Structures and vibrational frequencies in the full configuration interaction limit: Predictions for four electronic states of methylene using a triple-zeta plus double polarization (TZ2P) basis

Benchmark energies, geometries, dipole moments, and harmonic vibrational frequencies are determined for four states of methylene (CH2) by solving the electronic Schrödinger equation exactly for a triple-ζ plus double polarization (TZ2P) basis with the restrictions that the core orbital remains doubly occupied and the highest-lying virtual orbital is deleted. Approximate models of electron correlation are evaluated based on their ability to match the exact, full configuration interaction results. Predictions from configuration interaction with all single, double, triple, and quadruple substitutions (CISDTQ) and coupled-cluster including singles, doubles, and triples (CCSDT) are virtually identical to the full CI results for all but the c̃ 1A1 state, which is poorly described by a single-configuration reference. In agreement with previous work, the c̃ state remains slightly bent at the TZ2P full CI level of theory, with a bond angle of 170.1° and a barrier to linearity of only 25 cm−1.

Full configuration interaction benchmarks for the ?3B1, ã 1A1, ? 1B1 and ? 1A1 states of methylene

Abstract Previous experimental and theoretical work on the four lowest lying electronic states of methylene is summarized and new benchmark energies, geometries, dipole moments and harmonic vibrational frequencies are obtained by solving the electronic Schrodinger equation exactly, given a double-ζ plus polarization (DZP) basis set and restricting the core orbital to remain doubly occupied. These full configuration interaction (CI) results are used to evaluate several approximate treatments of electron correlation. The predictions of a CI procedure including all single, double, triple and quadruple excitations (CISDTQ) are virtually identical to the full CI results for all but the c 1 A 1 state, which is the second state of its symmetry and as such is difficult to describe using standard single-reference methods.

Computation of ionization potentials using the unitary group based open-shell coupled-cluster theory

The unitary group based open-shell state specific (SS) coupled-cluster (CC) theory is used to compute energies and ionization potentials for several electronic states of methylene, using a double-zeta plus polarization basis set model. The results are compared with the exact full configuration interaction (FCI) solutions as well as with various limited CI results. It is found that the open-shell SS CC theory yields similar results to those obtained by CI involving up to and including triple excitations. The error in calculated ionization potentials never exceeds half an electron volt.

Two new electronic states of methylene

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTwo new electronic states of methyleneKarl K. Irikura, Russell D. Johnson III, and Jeffrey W. HudgensCite this: J. Phys. Chem. 1992, 96, 15, 6131–6133Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July 1992https://doi.org/10.1021/j100194a010RIGHTS & PERMISSIONSArticle Views120Altmetric-Citations22LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (411 KB) Get e-Alerts

Ab initio rotation-vibration transition moments for CH 2 in the [formula omitted] and [formula omitted] electronic states

Ab initio dipole moments have been computed at nine nuclear geometries for both the X ̃ 3B 1 and a ̃ 1A 1 electronic states of methylene (CH 2). These values have been used to calculate the dipole moments and some rotation-vibration transition moments for both states. The transition moments for the ν 1 and ν 3 fundamental bands in the X ̃ 3B 1 state are found to be very small (both ⋍ 0.003 D) whereas they are quite large in the a ̃ 1A 1 state (0.098 and 0.070 D, respectively). The dipole moment of the a ̃ 1A 1 state is calculated to be 1.7 D, which is three times larger than that of the X ̃ 3B 1 state.