Theoretical Analysis of L-proline Trichloroacetate Optical Materials
 The optimized molecular structure, natural bond orbitals (NBO) analysis, HOMO-LUMO analysis and nonlinear optical properties of the L-proline trichloroacetate molecule have been calculated by the density functional theory (DFT) method using the B3LYP function with the 6-31G(d) basis set. INTRODUCTION Recently, crystal growth and detailed characterization on the properties of L-proline trichloroacetate (LPTC) crystal, a salt of the amino acid L-proline, have been reported [1, 2]. Proline, one of the 20 naturally occurring amino acids, has a peculiar structure, since it is the only cyclic amino acid among them; the amino group is part of a pyrrolidine ring, making it less flexible, restricting the local conformation freedom, and lowering the number of possible conformers. The ability of proline to form different intramolecular hydrogen bonds is due to its conformational versatility, caused by the capacity of reorientation of both −COOH and imine groups [3]. In the present work, quantum chemical computations based on the density functional theory (DFT) have been performed. The optimized molecular geometry, HOMO-LUMO and natural bond orbital analysis, the first hyperpolarizability (β0) and related properties (μ, α0) were calculated. COMPUTATIONAL METHODS DFT computations were performed by using the closed-shell Becke-Lee-Yang-Parr hybrid exchange-correlation three-parameter functional (B3LYP) in combination with 6-31G(d) basis set to derive the complete geometry optimizations and normal-mode analysis on isolated entities [4, 5]. The first task of the computational work was to determine the optimized geometry (Fig.1), which represents an isolated molecule with stationary points in the potential surface; no imaginary frequencies were obtained which confirms the convergence. Xiaojing Liu a* , Xin Sun School of Physics and Technology, University of Jinan, Jinan 250022, Shandong Province, PR China a lxj@mail.sdu.edu.cn