Ab initio determination of crystal stability of di-p-tolyl disulfide

Abstract

With the rapid growth of energy demand and the depletion of existing energy resources, the new materials with superior performances, low costs and environmental friendliness for energy production and storage are explored. Di-p-tolyl disulfide (p-Tol2S2) is a typical lubricating material, which has been applied in the field of energy storage. The conformational properties and phase transformations of p-Tol2S2 have been studied by pioneers, but their polymorphs and the polymorphism induced crystal structure changes require further analysis. In this study, we perform the crystal structural screening, prediction and optimization of p-Tol2S2 crystal with quantum mechanical calculations, i.e., density functional theory (DFT) and second-order Møller–Plesset perturbation (MP2) methods. A series of crystal structures with different molecular arrangements are generated based on the crystal structure screening. As compared to long-established lattice energy calculation, we take an advantage of using more accurate technique, which is Gibbs free energy calculation. It considers the effects of entropy and temperature to predict the crystal structures and energy landscape. By comparing the Gibbs free energies between predicted and experimental structures, we found that phase α is the most stable structure for p-Tol2S2 crystal at ambient temperature and standard atmospheric pressure. Furthermore, we provide an efficient method to discriminate different polymorphs that are otherwise difficult to be identified based on the Raman/IR spectra. The proposed work enable us to evaluate the quality of various crystal polymorphs rapidly.

Phase Transitions and Stabilities among Three Phases of Di-p-tolyl Disulfides

“…It is a potent tool for the physical evaluation of pharmaceutical solids, especially when performed using the Fourier transform method (FT–IR or FT–Raman) [ 52 ]. In one of our previous articles, Raman spectra of p-Tol 2 S 2 phases α and β were covered in detail [ 44 ]. Therefore, only IR spectra are provided here.…”

“…FT–IR spectra are frequently employed to evaluate the type of polymorphism present in a pharmaceutical substance [ 53 ]. The DFT computational methods have been successfully used to predict FT–IR spectra of different pharmaceutical crystals [ 44 , 48 , 50 ]. Here, for comparison, we provide FT–IR of three phases of p-Tol 2 S 2 .…”

“…Since organic compounds typically have enormous molecular sizes, the conventional ab initio computational technique does not work with them. Therefore, we used the embedded fragmentation quantum mechanical approach [ 41 , 42 , 43 , 44 ]. It is a technique that divides the internal energy of a p-Tol 2 S 2 crystal into appropriate mixtures of monomers and overlapping dimer energies that are incorporated in the electrostatic field of the crystalline environment [ 44 ].…”

“…Therefore, we used the embedded fragmentation quantum mechanical approach [ 41 , 42 , 43 , 44 ]. It is a technique that divides the internal energy of a p-Tol 2 S 2 crystal into appropriate mixtures of monomers and overlapping dimer energies that are incorporated in the electrostatic field of the crystalline environment [ 44 ]. The Hartree–Fock level embedding field, which consists of self-consistently determined atomic charges, is a crucial technique.…”

Solid–solid phase transformation of aspirin at high pressures and room temperatures

“…Generally, the molecular size of drug molecules is large, and the traditional ab initio method cannot be applied to macromolecular systems. Hence, we applied the embedded-fragment quantum mechanical method (He et al, 2014;Liu et al, 2017;Luo et al, 2019;Han et al, 2021Han et al, , 2022, which divides the internal energy per unit cell of the aspirin crystal into an appropriate combination of the energies of the monomers and overlapping dimers that are embedded in the electrostatic field of the rest of the crystalline environment (Li et al, 2015;Hao et al, 2021Hao et al, , 2019. The process of breaking down the embedded field is essential and, in our method, the field consists of self-consistently determined atomic charges at the Hartree-Fock level.…”