Theoretical investigation of the dispersion interaction in argon dimer and trimer

Abstract

The ultimate aim of the present work is to establish an acceptable level of computation for the van der waals (vdw) complexes that is able to pick up appreciable amount of dispersion interaction energy, reproduce the equilibrium separation within the acceptable limits and at the same time cost and time effective. In order to reach this aim vdw clusters where pure isotropic dispersion interaction occur, namely, Ar dimer and trime were investigated. Computations using different basis sets and at different levels of theory have been carried out. Three basis sets, namely, the 6-31++G ** , the 6-311++G ** and the aug-cc-pvdz basis set, were found superior to all other basis sets used. The high performance and relative small CPU time of the 6-31++G ** basis set make it a good candidate for use with large vdw clusters, especially those of interest in biology. Three compound methods were applied in the present work, namely G1, G2 and G2 Moller-Plesset (MP2) and the complete basis set method, CBS-Q. These methods failed to detect the attraction dispersion interaction in the dimer. The predicted repulsive interaction seems dominant in all these methods. Some of the recently developed Density Functional Theory (DFT) methods that were parameterized to account for the dispersion interaction were also evaluated in the present work. Results come to the conclusion that, in contrast to the claims made, state-of-theart Density Functional Theory methods are incapable of accounting for dispersion effects in a quantitative way, although these methods predict correctly the inter-atomic separations and are thus considered a real improvement over the conventional methods. BS-SE has been computed, analyzed and discussed.

Equilibrium Thermal Physics of Noble Gases

“… For practitioners it is important to operate with advanced mathematical models of noble gases to improve the controllability and repeatability of precise technological processes, such as production of semiconductor crystals and devices in controllable inert atmosphere [2] or utilization of noble gases in the precise metrology [3]. Widely used theoretical models of atomic interactions in real gases, such as the famous Lennard-Jones approach [4], consider the atoms of noble gases as round spheres and do not take into consideration the angular dependence of their interaction potential [5]. It will be shown here that this assumption meets a contradiction with experimental results.…”

“…One of aims of this work is to apply the recently developed thermal analysis method [6] to noble gases for estimation of their pair interaction parameters with a due precision. This thermal analysis of precise experimental thermophysical data for pure gases shows that even in noble gases the pair atomic interaction cannot be reduced to the round sphere model [6].…”

“…One of aims of this work is to apply the recently developed thermal analysis method [6] to noble gases for estimation of their pair interaction parameters with a due precision. This thermal analysis of precise experimental thermophysical data for pure gases shows that even in noble gases the pair atomic interaction cannot be reduced to the round sphere model [6]. The discovered here growth of the dimers' bond energy in noble gases at low temperatures tells about the mutual orientation of atoms in gaseous dimers due to the lack of rotational symmetry of their outer electronic shells.…”

“…Our approach is phenomenological and is opposite to the microscopic simulations of the many particle systems with model interaction potentials [5,11]. It is directed towards the clarification of the atomic and molecular interaction details and utilizes only one assumption that the available databases with regularized thermophysical data are precise enough to provide the estimation of the atomic and molecular interaction parameters with an acceptable precision.…”

“…The knowledge that we may gain of their molecular constitution may then be utilized in the search for formulas to represent their observable properties [12]." To the contrary, as it is seen from the work [5], the precision of assumptions about the interaction potential and its parameters, even for atomic gases, is crucial for the simulation methods: the smallest deviations in the model potential result in a large spread of the found atomic interaction parameters.…”