Abstract
The Lennard–Jones (LJ) and Improved Lennard–Jones (ILJ) potential models have been deeply tested on the most accurate CCSD(T)/CBS electronic energies calculated for some weakly bound prototype systems. These results are important to plan the correct application of such models to systems at increasing complexity. CCSD(T)/CBS ground state electronic energies were determined for 21 diatomic systems composed by the combination of the noble gas atoms. These potentials were employed to calculate the rovibrational spectroscopic constants, and the results show that for 20 of the 21 pairs the ILJ predictions agree more effectively with the experimental data than those of the LJ model. The CCSD(T)/CBS energies were also used to determine the parameter of the ILJ form, related to the softness/hardness of the interacting partners and controlling the shape of the potential well. This information supports the experimental finding that suggests the adoption of for most of the systems involving noble gas atoms. The He-Ne and He-Ar molecules have a lifetime of less than 1ps in the 200–500 K temperature range, indicating that they are not considered stable under thermal conditions of gaseous bulks. Furthermore, the controversy concerning the presence of a “virtual” or a “real” vibrational state in the He molecule is discussed.
Highlights
The detailed characterization of several equilibrium and non-equilibrium properties of matter is often obtained through the proper formulation of force fields associated with non-covalent intermolecular interactions [1]
From this table it is possible to note that the equilibrium distances calculated with CCSD(T)/complete basis set (CBS) level agree more effectively with experimental data [20,46]
These results show that the best agreement between theoretical and experimental data happens with the CCSD(T)/CBS level, mainly when compared with the data available in [20,47]
Summary
The detailed characterization of several equilibrium and non-equilibrium properties of matter (in condensed and gaseous phases) is often obtained through the proper formulation of force fields associated with non-covalent intermolecular interactions [1]. The adoption of simple and accurate models of this type of interactions, to be used in molecular dynamics simulations of both ionic and neutral aggregates, still represents a basic question Such models must be given in the analytical form, from which the first and second derivative of the interaction, defining force, and force constant must be obtained and must present continuity of behavior. They must involve few parameters having a defined physical meaning that can be used as proper scaling factors when the extension to systems at increasing complexity is attempted. These alternative models use a combination of complicated functions and with many adjustable parameters
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