On the determination of Lennard-Jones parameters for polyatomic molecules

Abstract

Characterizing the key length and energy scales of intermolecular interactions, Lennard-Jones parameters, i.e., collision diameter and well depth, are prerequisites for predicting transport properties and rate constants of chemical species...

Theoretical studies on Lennard-Jones parameters of benzene and polycyclic aromatic hydrocarbons

“…The impact on the L-J self-collision parameters from using different bath gases He and N 2 seems to be bigger for σ – ε than for SA and η – ξ , indicating that SA and η – ξ may be more reasonable. To be noted, we do not have L-J parameters by SA for PAHs with molecular mass larger than 300 g mol −1 , because it is very time-consuming to obtain intermolecular potentials at all sampling points, however the computing time is about one order of magnitude shorter for σ – ε and η – ξ , because an iterative search algorithm 13 was used to efficiently find σ and ε on relative orientations. Hence, the η – ξ method seems to be both reliable and efficient for computing L-J parameters for PAHs.…”

“…Recently, we proposed a new orientation-averaging rule called the η – ξ method, 13 on the basis of two characteristic variables η and ξ , representing the repulsive and attractive energy scales, respectively, as shown in eqn (7). η n = ε n σ 12 n , n = 1, 2, 3…, N Ω ξ n = ε n σ 6 n , n = 1, 2, 3…, N Ω in which σ n and ε n are calculated by eqn 6(a) and (b). Subsequently, the effective L-J parameters σ and ε can be derived from η and ξ as follows. σ = ( η / ξ ) 1/6 ε = ( ξ 2 / η )…”

“…Recently, we proposed a new orientation-averaging rule called the h-x method, 13 on the basis of two characteristic variables h and x, representing the repulsive and attractive energy scales, respectively, as shown in eqn (7).…”

“…More details of various methods can be found from the review of Lendvay. 12 In our recent study of effective L-J parameters, 13 we developed an orientationaveraging rule based on two characteristic variables h and x representing repulsive and attractive energy scales separately. Compared with the binary diffusion coefficients predicted by SA and 1DM, those using this new rule (called the h-x method) agree better with experimental data from McGivern et al, [14][15][16][17] who measured the diffusion coefficients of n-alkanes from methane to n-octane in helium and nitrogen using reversed-ow chromatography.…”

“…This is reasonable because intermolecular interactions are better captured by explicitly averaging the characteristic repulsive and dispersive energies. In addition, an iterative search algorithm 13 was developed to robustly and efficiently find the collision diameter and well depth on an arbitrary orientation of the intermolecular potential energy surfaces, which greatly shortened the computation time.…”