TY - JOUR

T1 - First-principles calculations on anharmonic vibrational frequencies of polyethylene and polyacetylene in the approximation

AU - Kȩeli, Murat

AU - Hirata, So

AU - Yagi, Kiyoshi

N1 - Funding Information:
This work was supported by the U.S. National Science Foundation (Grant No. CHE-0844448), the U.S. Department of Energy (Grant No. DE-FG02-04ER15621), the Donors of the American Chemical Society Petroleum Research Fund (Grant No. 48440-AC6), and the MEXT, Japan (Supra Functional Systems 477). S.H. is a Camille Dreyfus Teacher-Scholar. We thank the University of Florida High-Performance Computing Center for a generous allocation of CPU time.

PY - 2010/7/21

Y1 - 2010/7/21

N2 - The frequencies of the infrared- and/or Raman-active (k=0) vibrations of polyethylene and polyacetylene are computed by taking account of the anharmonicity in the potential energy surfaces (PESs) and the resulting phonon-phonon couplings explicitly. The electronic part of the calculations is based on Gaussian-basis-set crystalline orbital theory at the Hartree-Fock and second-order Møller-Plesset (MP2) perturbation levels, providing one-, two-, and/or three-dimensional slices of the PES (namely, using the so-called n -mode coupling approximation with n=3), which are in turn expanded in the fourth-order Taylor series with respect to the normal coordinates. The vibrational part uses the vibrational self-consistent field, vibrational MP2, and vibrational truncated configuration-interaction (VCI) methods within the approximation, which amounts to including only k=0 phonons. It is shown that accounting for both electron correlation and anharmonicity is essential in achieving good agreement (the mean and maximum absolute deviations less than 50 and 90 cm-1, respectively, for polyethylene and polyacetylene) between computed and observed frequencies. The corresponding values for the calculations including only one of such effects are in excess of 120 and 300 cm-1, respectively. The VCI calculations also reproduce semiquantitatively the frequency separation and intensity ratio of the Fermi doublet involving the V2 (0) fundamental and V8 (π ) first overtone in polyethylene.

AB - The frequencies of the infrared- and/or Raman-active (k=0) vibrations of polyethylene and polyacetylene are computed by taking account of the anharmonicity in the potential energy surfaces (PESs) and the resulting phonon-phonon couplings explicitly. The electronic part of the calculations is based on Gaussian-basis-set crystalline orbital theory at the Hartree-Fock and second-order Møller-Plesset (MP2) perturbation levels, providing one-, two-, and/or three-dimensional slices of the PES (namely, using the so-called n -mode coupling approximation with n=3), which are in turn expanded in the fourth-order Taylor series with respect to the normal coordinates. The vibrational part uses the vibrational self-consistent field, vibrational MP2, and vibrational truncated configuration-interaction (VCI) methods within the approximation, which amounts to including only k=0 phonons. It is shown that accounting for both electron correlation and anharmonicity is essential in achieving good agreement (the mean and maximum absolute deviations less than 50 and 90 cm-1, respectively, for polyethylene and polyacetylene) between computed and observed frequencies. The corresponding values for the calculations including only one of such effects are in excess of 120 and 300 cm-1, respectively. The VCI calculations also reproduce semiquantitatively the frequency separation and intensity ratio of the Fermi doublet involving the V2 (0) fundamental and V8 (π ) first overtone in polyethylene.

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U2 - 10.1063/1.3462238

DO - 10.1063/1.3462238

M3 - Article

C2 - 20649311

AN - SCOPUS:77956233191

SN - 0021-9606

VL - 133

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

IS - 3

M1 - 034110

ER -