DFT studies for optoelectronic properties of pure l-alanine and doped with Li

Structural and optoelectronic properties of the pure l-alanine (CH₃CHNH₂COOH) and substituted with Li in two different sites CH₃CHNHLiCOOH (basic) and CH₃CHNH₂COOLi (acidic) are systematically investigated by the density functional theory (DFT). We have used WIEN2k and Gaussian 09W codes for structural optimization. The optimized lattice constants are found to be consistent with the experimental results. l-Alanine is a wide indirect band gap compound and hence is an attractive material for optoelectronic applications. The calculated fundamental band gaps for CH₃CHNH₂COOH, CH₃CHNHLiCOOH and CH₃CHNH₂COOLi are found to be 4.85, 3.50 and 2.40 eV, respectively. Obtained band gap value of 4.85 eV for l-alanine is in coincidence with the experimental (4.67 eV) and theoretical results (4.54 and 5.07 eV). Substitution of Li with H element in COOH chain, the transition from an indirect to direct band gap has been observed in sample. Optical properties such as dielectric functions and energy loss functions are also evaluated and discussed in detail.