DFT-Study of Structural, Mechanical, and Electronic Properties of L-leucine under Pressure

Abstract

In this paper, the study of the properties of L-leucine crystal is carried out using the density functional theory with PBE exchange-correlation functional with consideration of the van der Waals forces according to the Grimme scheme in option D3 (BJ). The calculations are based on the linear combination method of atomic orbitals and performed using the CRYSTAL’17 software package. The structural and electronic properties of L-leucine crystal under pressure are investigated, and the equation of state for the pressure ranges from 0 to 4 GPa is obtained. The constructed equation of state shows that anomalies are observed due to changes in the unit cell parameter a directed across the layers of molecules, as well as due to the angle p. It has been suggested that a possible complication of the structure of L-shaped amino acid molecules by functional groups is associated with the bulk modulus B0 and its first derivative B1. Using the calculated compressibility modulus as an example, it is shown that the highest compressibility is observed along the c axis, which directed along the orientation of the molecules in the unit cell of the L-leucine crystal. The observed compressibility is four and five times higher than the compressibility in L-alanine and L-threonine, respectively. An analysis of the dependence of electronic properties on pressure, such as the effective charges of functional groups, the band gap, and the location of the peaks of the density of states, demonstrates that the above properties do not undergo noticeable changes in the pressure range from 0 to 4 GPa.