Interchain Interaction in Semiconducting Liquid and Amorphous Selenium

Abstract

Semiconducting liquid and amorphous selenium (l-Se,a-Se), which are representative disordered materials, are regarded as assemblies of two-coordinated chains. The atomic and electronic structures have been studied theoretically using ab initio and tight-binding molecular-dynamics (MD) or Monte Carlo methods. However, the former is difficult to apply to a large system size, and the latter is difficult to deal with intermolecular interactions appropriately. A classical chain model 1) has been also applied to study the atomic structure and dynamics. It assumes, however, an isotropic Lenard-Jones potential (LJ) as the interaction between the nonbonded atoms. Since each Se atom in the chains has a p-lone pair (LP), the interaction between the nonbonded atoms is anisotropic in practice. We construct a chain model including the anisotropy based on an ab initio molecular-orbital (MO) method, and obtain the structural samples by MD simulations. We compute the intra and intermolecular potential of Se clusters using an ab initio MO method (MP2/CEP-31G(d)). Potentials of an isolated Se chain (HSe10H) are calculated around the optimized geometry, and fitted to a valence force field model. The bending force constant is similar to that of Ref. 1). The barrier of internal rotation is 163 meV that is about 2.4 times as large as the corresponding value of Ref. 1). In our MD simulations, we scale the calculated stretching force constant by 0.7 to explain the experimental stretching modes. Intermolecular potentials are calculated for (HSe3H)2 dimer. They are closely related to the way of facing between the LPs on the central Se atom in the monomer, which causes 0.3 A change of the atomic effective radius on the interaction. The interaction potential of the pair of nonbonded atoms i and j is represented by