Estudo teórico baseado na teoria do funcional da densidade das propriedades estruturais, eletrônicas e ópticas dos cristais de sarcosina e DL-alanina em função da pressão

Abstract

The study of the structural and electronic properties of amino acid crystals under different pressure conditions is highly relevant, as these materials have potential for technological applications. Understanding how pressure influences the characteristics of organic crystals can lead to significant advances in the development of new compounds and the optimization of industrial processes. Thus, this research not only advances theoretical knowledge about these systems but also paves the way for technological innovations. The methodology adopted for the computational calculations in this study is based on Density Functional Theory (DFT), using the Quantum ESPRESSO software. The Projector Augmented Wave

(PAW) method was employed to perform the computational calculations, and the exchange- correlation components were described using the Perdew-Burke-Ernzerhof (PBE/GGA),

PBE for solids (PBEsol/GGA), revised PBE (revPBE/GGA), and the non-local van der Waals correlation functional (vdW-DF). Additionally, the Grimme D3 dispersion term was applied in conjunction with all GGA functionals to correct for dispersion interactions. Geometry optimization was considered converged at 10−3 eV· Å−1 . In this research, the structural and electronic properties of sarcosine and DL-alanine crystals were investigated under extreme hydrostatic pressure conditions, with special attention to lattice parameters and hydrogen bond behavior. For sarcosine, discrete pressure points ranging from 0.0 to 3,7 GPa were used, while for DL-alanine the applied pressure ranged from 0,0 to 18 GPa. The computational results for the optimized lattice parameters a, b, and c and the volume of sarcosine at ambient pressure show deviations of less than 2% compared to experimental values reported in the literature. Regarding electronic properties, sarcosine exhibits a direct band gap at ambient pressure (along the Γ point). The calculated band gap was approximately 5.20 eV, indicating insulating behavior in this configuration. Under pressure, sarcosine displays anisotropic behavior and a theoretical bulk modulus B0 of about 6.98 GPa. Furthermore, the band gap of sarcosine does not decrease monotonically with pressure; it initially decreases from 5,20 eV to 4,90 eV up to approximately 1,4 GPa, then slightly increases, reaching 5,05 eV at 3,7 GPa. This non-linear behavior is interpreted as a result of competition between unit cell contraction and molecular rotation within the crystal. In terms of optical properties, the static dielectric constant showed values of 2,08 in the xx plane, 2,47 in the yy plane, and 2,17 in the zz plane, with the highest polarity in the yy plane, reinforcing the system’s anisotropic behavior. Strong absorption in the ultraviolet region indicates potential application as ultraviolet light polarizers. For DL-alanine, the computational results for the optimized lattice parameters and unit cell volume decrease continuously with increasing pressure, showing excellent agreement with available experimental data. Additionally, the b parameter decreased by approximately 14%, indicating greater flexibility of the crystal in this direction. Under pressure up to 18 GPa, DL-alanine exhibits anisotropic behavior and a theoretical bulk modulus B0 of

about 8.48 GPa. Regarding the theoretical value of the crystalline dipole moment, the value obtained at ambient pressure was approximately 75 Debye, while above 15 GPa a sharp drop is observed, reaching approximately 38 Debye at 17,5 GPa. The voids are also drastically minimized, ranging from 84,76 Å3 at ambient pressure to values below 3,94 Å3 at pressures above 16,4 GPa - a reduction of approximately 95%. The results presented here are essential for a deeper understanding of the potential technological applications of sarcosine and DL-alanine in different scenarios, highlighting the relevance

of theoretical studies dedicated to the investigation of crystalline systems under high- pressure conditions. This research deepens the understanding of intermolecular interactions,

as well as the optical, structural, and electronic properties of organic crystals, establishing a solid foundation for future investigations in the field of materials science.