Calibration of 119Sn isomer shift using ab initio wave function methods.

The isomer shift for the 23.87 keV M1 resonant transition in the (119)Sn nucleus is calibrated with the help of ab initio calculations. The calibration constant alpha((119)Sn) obtained from Hartree-Fock (HF) calculations (alpha(HF)((119)Sn) = (0.081+/-0.002)a(0)(-3) mm/s) and from second-order Moller-Plesset (MP2) calculations (alpha(MP2)((119)Sn) = (0.091+/-0.002)a(0)(-3) mm/s) are in good agreement with the previously obtained values. The importance of a proper treatment of electron correlation effects is demonstrated on the basis of a statistical analysis of the results of the calibration. The approach used in the calibration is applied to study the (119)Sn isomer shift in CaSnO(3) perovskite under pressure. Comparison with the experimental results for the pressure range of 0-36 GPa shows that the current methodology is capable of describing tiny variations of isomer shift with reasonable accuracy.