Structural Composition of First-Neighbor Shells in GeSe2 and GeSe4 Glasses from a First-Principles Analysis of NMR Chemical Shifts

Isotropic chemical shifts and quadrupole coupling parameters of Se-77 and Ge-73 nuclei in GeSe2 and GeSe4 glasses are determined through density-functional NMR calculations on amorphous model structures generated by ab initio molecular dynamics. The comparison with experimental NMR spectra enables structural assignments for Se-77 chemical shifts, pointing to fractional compositions of nearest-neighbor coordinations which are consistent with both neutron diffraction and NMR experiments.