Optical properties of sarcosine crystal under hydrostatic pressure: a DFT-based computational study

Organic crystals have become attractive for applications as nonlinear optical materials due to their nonlinear susceptibility, optical transparency, and other properties that can be tuned using elevated pressure. We have investigated the optical properties of the zwitterionic crystal of the natural amino acid sarcosine using the first-principles projected augmented plane wave method and the GGA and hybrid exchange-correlation functionals. The molecular crystal of sarcosine is composed of zwitterion organic molecules arranged in an antiparallel fashion by the formation of distinct hydrogen bond chains in the planes (100), (010), and (001). The calculated anisotropic optical properties of sarcosine, including the dielectric constant, absorption, extinction coefficient, refractive index, reflectivity, energy loss function, and optical conductivity, are determined from ambient to 3.7 GPa hydrostatic pressure along crystallographic axes a, b, and c. Sarcosine has an optical anisotropy at ambient and external hydrostatic pressures, characterized by specific peaks in the ultraviolet spectrum. The results show the potential application of the studied system in nonlinear optics, UV detectors, and high-pressure photonic applications.