L-arginine semi-oxalate (LASO) molecule [C6H15N4O2 + .C2HO4 -] was synthesized and its IR and 1 H NMR and 13 C NMR spectroscopy were studied by P. Vasudevan et al. In this study, the geometric structure determination of LASO molecule was optimized to obtain its molecular geometric structure by using the Gaussian program. The theoretical harmonic vibrational wavenumbers of LASO molecule were also calculated. The calculated theoretical data were checked with the experimental data. The

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... and the theoretical data were seen compatible with each other. Further more; LASO molecule is studied by means of NMR spectra. Finally, the analysis of nonlinear optical (NLO) properties, molecular orbitals (MO), molecular surfaces and Mulliken, APT and NBO populations were viewed. All theoretical calculations have been fulfilled by employing the Density Functional Theory (DFT) at B3LYP/6-311++G(d,p) and HSEH1PBE/6-311++G(d,p) levels.