Energy Convergence in a Structure Optimization and Vibrational Modes of Some Acene Molecules

Abstract

Acene molecules, exhibit interesting electronic and structural properties due to the presence of alternating single and double bonds. There has been a recent surge in interest in studying small acenes, such as anthracene, tetracene, and pentacene. Geometry optimization and energy convergence for acene molecules are essential steps in understanding their properties and behavior. The modellings of MJs was done using Jmol computer code and the geometry of these structures was relaxed towards its minimum energy using a two-step procedures which are; pre-relax the structure with light settings and post-relaxation run using tight settings down to 10-2 eV/Å stopping criteria. The results showed that total energy uncorrected and the maximum force converged. The converged energies for anthracene, tetracene and pentacene molecules are, 0.0057 eV/Å, 0.0056 eV/Å, and 0.0060 eV/Å respectively. For the vibrational analysis, some of the results indicated that the input geometry is indeed a local minimum and not a saddle point. The results also showed a low IR absorption, with maximum intensity of 1.83 D2Å-2, 2.00 D2Å-2, and 1.91 D2Å-2 for anthracene, tetracene, and pentacene respectively.