outer-valence green’s function study on small biomolecules

Here, a theoretical study of electronic structures of conformers of vitamin c was studied in the gas phase# outer-valence green's function (ovgf) methodology employing with 6-311g++(d,p) basis set was used for the calculations# the stable conformers were selected by thermochemistry calculations and the ionization energies were obtained for them# also, these results have been compared with another ionization method, for example, sac-ci calculations# the comparison of two spectra shows that ovgf results are in better with experimental data for moieties of vitamin c# so the sac-ci spectra were shifted along the ionization energy scale to enable the first band in sac-ci spectrum to match the first band in corresponding ovgf spectrum# natural bonding orbital (nbo) study was performed for analyzing each band of ionization# nbo calculations showed that the first ionization band of vitamin c was related to the  electrons of the c=c bond of the ring in the structure of the molecule#