doi:10.1016/j.cplett.2005.03.049
Copyright © 2005 Elsevier B.V. All rights reserved.
Electronic polarization in liquid acetonitrile: A sequential Monte Carlo/quantum mechanics investigation
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Roberto Rivelinoa, B.J. Costa Cabralb, c, Kaline Coutinhod and Sylvio Canutod, 
, 
aInstituto de Física, Universidade Federal da Bahia, 4210-340 Salvador, BA, Brazil
bDepartamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal
cGrupo de Física Matemática da Universidade de Lisboa, Av. Professor Gama Pinto 2, 1649-003 Lisboa, Portugal
dInstituto de Física, Universidade de São Paulo, CP 66318, 05315-970 São Paulo, SP, Brazil
Received 23 February 2005;
revised 23 February 2005.
Available online 1 April 2005.
Abstract
The electronic polarization of liquid acetonitrile is investigated using the sequential Monte Carlo/quantum mechanics methodology. Second-order Møller–Plesset and density-functional theory calculations of the dipole moment are performed on statistically uncorrelated structures of liquid acetonitrile generated by the MC simulation. Our best result, obtained at the MP2/aug-cc-pVTZ level, gives an average dipole moment of 4.65 ± 0.19 D, in agreement with an experimental prediction of 4.5 ± 0.1 D. This result corresponds to an increase of 0.71 ± 0.19 D in going from the gas to the liquid state.
Fig. 1. The acetonitrile molecule and definition of the atomic indices used in Table 1.
Fig. 2. Statistical distribution of calculated dipole moments of acetonitrile. Results obtained using MP2/aug-cc-pVTZ calculations in the largest structure considered (1 + 253). Also shown are the gas phase calculated value and the experimentally inferred value.
Fig. 3. Statistical convergence of the calculated dipole moment of liquid acetonitrile. Individually calculated values (a) and accumulated average (b) with statistical error are shown. Results obtained using MP2/aug-cc-pVTZ calculations in the largest structure considered (1 + 253).
Table 1.
Intermolecular potential [16] used for acetonitrile (see Fig. 1)
Table 2.
Comparison of the calculated dipole moments (D) using MP2 and DFT methods for different structures of acetonitrile
The dipole moments correspond to averages over 50 QM calculations using uncorrelated structures generated by MC simulation. Values are given as 
μ
± σ, where μ is the average dipole moment of the configuration and σ is the standard deviation.
Table 3.
Calculated changes in the dipole moment (D) using MP2 and DFT methods for different radii (in Å)
Values are given as average gas-to-liquid dipole moment change, Δμ ± σ, where σ is the standard deviation.
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