A theoretical investigation on optimal structures of ethane clusters (C₂H₆)_n with n ≤ 25 and their building‐up principle

Abstract

Geometry optimization of ethane clusters (C(2)H(6))(n) in the range of n ≤ 25 is carried out with a Morse potential. A heuristic method based on perturbations of geometries is used to locate global minima of the clusters. The following perturbations are carried out: (1) the molecule or group with the highest energy is moved to the interior of a cluster, (2) it is moved to stable positions on the surface of a cluster, and (3) orientations of one and two molecules are randomly modified. The geometry obtained after each perturbation is optimized by a quasi-Newton method. The global minimum of the dimer is consistent with that previously reported. The putative global minima of the clusters with 3 ≤ n ≤ 25 are first proposed and their building-up principle is discussed.

Structural Features of Small Benzene Clusters (C6H6)n (n ≤ 30) As Investigated with the All-Atom OPLS Potential

“…At present, the global optimization of atomic/molecular clusters is one of the most difficult problems. Recently, the present author encountered a difficulty relating to molecular orientations in ethane clusters and modified the optimization algorithm. The global optimization is not performed routinely, and many articles have been published to improve efficiency of the global optimization. ,− …”

The structural investigation on small methane clusters described by two different potentials

“…Optimal geometries of methane clusters were searched with HMGP [28]. Starting geometries were generated by randomly placing molecules in a sphere with a radius of (3n/4π) 1/3 r e (a value of 3.8 Å is used for r e ).…”

“…Hence geometrical-perturbation operators [28] with subsequent local optimizations were used for searching lower-energy configurations.…”

“…The present author proposed an efficient geometry optimization method for atomic/molecular clusters (the Heuristic Method combined with Geometrical Perturbations, HMGP) [27,28]. In this work, the geometries of the methane clusters (CH 4 ) n with n ≤ 40 expressed by two different interatomic potentials are optimized with HMGP and geometrical features of the clusters are reported.…”

“…According to the studies on the ethane clusters [28], the orientation operator randomly modifies orientations of one and two molecules three and nine times, respectively. The methane molecule takes higher symmetry than the ethane molecule.…”