Ab initio, Xα and IEHT Mo calculations of Mössbauer spectroscopy parameters for iron carbonyls

Calculations of charge density and the electric field gradient tensor at the iron nucleus by means of ab initio LCAO SCF, MS-X_α, SCC-X_α and IEHT methods for iron carbonyls Fe(CO)n, n=1-5, are presented. The calculated EFG values for the closed-shell molecule Fe(CO)5 show reasonable agreement with experiment while the values obtained for the open-shell molecules Fe(CO)n, n=1-4, significantly depend on the calculational method. Ab initio results, though using a minimal basis set, are closer to experimental data than X_α and IEHT results.