Polarizable Models in Molecular Dynamics for Identification of Effective Properties

Abstract

The importance of mathematical modeling of modern materials is emerged due to high cost of test samples and dependence of created samples on pre-modeling. Today scientists tend to develop such research methods that describe test samples as accurately as possible. In this chapter, we describe two highly-effective methods of molecular dynamics (MD) : (i) Fluctuating charge method and (ii) Effective moduli method. The first one is used for modeling of polarization effect by combining charge equilibration with electronegativity principle. The second one is used in mechanics for identification of homogeneous materials and composites properties. Computational experiments were performed using the LAMMPS software. Test sample is a nanorod of zinc oxide. It was built on wurtzite basis cell with 8 basis atoms. COMB3 potential was chosen for its accuracy and capability of taking into account polarization effect. The sample is divided into 3 parts: loading area, “computational” area and fixation area. Our goal was to identify its piezoelectric effective constants and we used the next experiment: first we performed relaxation of the sample and then continued research with relaxation/loading periods. After each relaxation/loading stage, we computed piezoelectric effective constant using effective moduli method and after all stages were studied, we analyzed all results. We also investigated three different sizes of the sample to detect size effect. Results of computational experiments are given in tables and diagrams and correspond to other experiments in this area. Effective constant value tends to the value of this constant for crystal with increasing the sample size, demonstrating the expected size effect.