Theoretical investigations of optical properties of l-arginine trifluoroacetate crystal

In order to determine the molecular dipole moment (μ), polarizability (α), and first hyperpolarizability (β) of l-arginine trifluoroacetate (LATF) crystals, a series of basis sets including polarized and diffuse functions have been employed at the framework of Hartree–Fock and second order Möller–Plesset perturbation theory methods. The MP2/6-311++G(d,p) model predicts for the converged value of in-crystal dipole moment, polarizability and first hyperpolarizability are 21.2 D, 20.0 × 10−24 esu and 50.0 × 10−31 esu, respectively. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Electronic excitation properties are discussed within the framework of the two-level model on the basis of an orbital analysis. The coupled perturbed Hartree–Fock (CPHF) procedure yields information on the dispersion behavior of first hyperpolarizability terms. The magnitudes of the various hyperpolarizability terms which describe the various second-order nonlinear processes show the following trend: β(−2ω;ω,ω) > β(0;ω,−ω) > β(0,0,0). By using the molecular structures and the molecular first hyperpolarizability, the components of second harmonic tensor coefficient d of the crystals were evaluated by the oriented-gas model.