Spectroscopic accuracy directly from quantum chemistry: Application to ground and excited states of beryllium dimer

Journal Article · Fri Mar 14 04:00:00 EDT 2014 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4867383· OSTI ID:22253453

Sharma, Sandeep; Booth, George H.; Yanai, Takeshi ^[1]; Umrigar, C. J. ^[2]

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1. Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, Okazaki, Aichi 444-8585 (Japan)
2. Laboratory of Atomic and Solid State Physics, Cornell University, New York 14853 (United States)

We combine explicit correlation via the canonical transcorrelation approach with the density matrix renormalization group and initiator full configuration interaction quantum Monte Carlo methods to compute a near-exact beryllium dimer curve, without the use of composite methods. In particular, our direct density matrix renormalization group calculations produce a well-depth of D{sub e} = 931.2 cm{sup −1} which agrees very well with recent experimentally derived estimates D{sub e} = 929.7±2 cm{sup −1} [J. M. Merritt, V. E. Bondybey, and M. C. Heaven, Science 324, 1548 (2009)] and D{sub e}= 934.6 cm{sup −1} [K. Patkowski, V. Špirko, and K. Szalewicz, Science 326, 1382 (2009)], as well the best composite theoretical estimates, D{sub e} = 938±15 cm{sup −1} [K. Patkowski, R. Podeszwa, and K. Szalewicz, J. Phys. Chem. A 111, 12822 (2007)] and D{sub e}=935.1±10 cm{sup −1} [J. Koput, Phys. Chem. Chem. Phys. 13, 20311 (2011)]. Our results suggest possible inaccuracies in the functional form of the potential used at shorter bond lengths to fit the experimental data [J. M. Merritt, V. E. Bondybey, and M. C. Heaven, Science 324, 1548 (2009)]. With the density matrix renormalization group we also compute near-exact vertical excitation energies at the equilibrium geometry. These provide non-trivial benchmarks for quantum chemical methods for excited states, and illustrate the surprisingly large error that remains for 1 {sup 1}Σ{sub g}{sup −} state with approximate multi-reference configuration interaction and equation-of-motion coupled cluster methods. Overall, we demonstrate that explicitly correlated density matrix renormalization group and initiator full configuration interaction quantum Monte Carlo methods allow us to fully converge to the basis set and correlation limit of the non-relativistic Schrödinger equation in small molecules.

• OSTI ID: 22253453
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 10 Vol. 140; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
74 ATOMIC AND MOLECULAR PHYSICS
ACCURACY
BERYLLIUM
BOND LENGTHS
CONFIGURATION INTERACTION
DENSITY MATRIX
DIMERS
EQUATIONS OF MOTION
EXCITATION
EXCITED STATES
MONTE CARLO METHOD
RENORMALIZATION