Intermolecular forces from density functional theory. III. A multiproperty analysis for the Ar(1S)-CO(1Σ) interaction

Abstract

The full anisotropic interaction between one Ar atom and the CO(1Σ) molecule treated as a rigid rotor (RR) at its equilibrium geometry is evaluated using density functional theory (DFT) to describe the short-range repulsive region (and its orientational anisotropy) as well as the well region and its angular dependence. The long-range dispersion forces are added from the results of perturbation theory and a scaling procedure is suggested for their correct matching with the DFT data. The computational results are found to agree very well with more sophisticated calculations and to improve on earlier empirical estimates. An extensive comparison with available transport property measurements is also carried out and using, among others, new experimental data for thermal diffusion [Shashkov et al., Inzh. Fiz. Zh. 71, 182 (1998)] analyzed in this work for the first time. The present modifications of DFT treatment of the interaction using the correct dispersion terms therefore appears to provide a realistic description of the Ar–CO potential and of several dynamical properties of this molecular mixture in the gas phase.

Rovibrational structure of the Ar–CO complex based on a novel three-dimensional ab initio potential

“…A physically more reasonable procedure, used in this paper although far more elaborate in terms of computational cost, is to retain the r dependence of the IPES and subsequently perform the dynamical calculations using the appropriately averaged IPES and rotational constant for each CO vibrational state. The standard approach utilizing an inherently adiabatic IPES has been used in all but the latest theoretical investigation of the Ar-CO van der Waals complex in which Gianturco and Paesani, 31 by means of a semiempirical density functional theory-based scheme for calculating IPESs, 29 showed that the diabatic couplings due to the IPES are indeed negligible for bound state calculations in the three lowest vibrational states of CO.…”

“…29 A novel feature of this IPES is that the CO bond was allowed to relax upon complex formation. Subsequently, neglecting diabatic couplings, this three-dimensional IPES was averaged over the lowest vibrational states of the free CO molecule.…”

“…The Ar-CO complex can be considered a prototype van der Waals system, as witnessed by the extensive experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and theoretical [20][21][22][23][24][25][26][27][28][29][30][31] work on its description. For example, the first paper, published in 1978 by Parker and Pack, 20 used Ar-CO as a model system for the development of electron gas methods for calculating intermolecular potential energy surfaces ͑IPESs͒.…”

“…Experimentally, the lower-lying levels comprising the ground state and the excited bending and stretching states are extensively characterized through the work of a number of authors, [2][3][4][5][6][7][8][9][10][11][12][13][14][15] whereas observations of higher-lying states have only recently been reported by Scheele, Lehnig, and Havenith. 16,17 On the theoretical side, a large part of the electronic structure methods, semiempirical 23,28,29,31 as well as ab initio, 24 -27,30 has been employed for calculating IPESs to assist in assigning experimental spectra. To this end, the most successful IPES is doubtlessly that computed by Jansen in 1994 24 using the coupled pair functional ͑CPF͒ method and later semiempirically extrapolated to give the ECPF IPES by the same author in 1996.…”

Perspectives from Quantum Chemistry for molecules and nanograins with astrophysical Interest

“…For instance, the M06-2X functional [102] is a highly non local functional with an enhanced contribution of non-local exchange completed with a meta-GGA correlation functional and was shown to provide reasonable results for noncovalent systems. In a more empirical scheme, the DFT energy can be corrected by an additional atom pair contribution to account for London dispersion through a −f (R)C 6 /R 6 term involving a short range cut-off f (R) [109][110][111][112][113][114][115][116]. ) and with the M06-2X functional [119].…”