Exploring new crystal structures of glycine via electric field-induced structural transformations with molecular dynamics simulations

Abstract

Being able to control polymorphism of a crystal is of great importance to many industries, including the pharmaceutical industry, since the crystal's structure determines significant physical properties of a material. While there are many conventional methods used to control the final crystal structure that comes out of a crystallization unit, these methods fail to go beyond a few known structures that are kinetically accessible. Recent studies have shown that externally applied fields have the potential to effectively control polymorphism and to extend the set of observable polymorphs that are not accessible through conventional methods. This computational study focuses on the application of high-intensity dc electric fields (e-fields) to induce solid-state transformation of glycine crystals to obtain new polymorphs that have not been observed via experiments. Through molecular dynamics simulations of solid-state α-, β-, and γ-glycine crystals, it has been shown that the new polymorphs sustain their structures within 125 ns after the electric field has been turned off. It was also demonstrated that strength and direction of the electric field and the initial structure of the crystal are parameters that affect the resulting polymorph. Our results showed that application of high-intensity dc electric fields on solid-state crystals can be an effective crystal structure control method for the exploration of new crystal structures of known materials and to extend the range of physical properties a material can have.