Evidence of strong electron correlation effects on thermal expansion in transition metals

The electronic contribution ${\alpha }_e$ to the thermal-expansion coefficient of Fe and Ni is investigated on the basis of a variational theory. This goes beyond the static approximation to the functional integral method by including electron correlations. The correlations greatly reduce the spontaneous volume magnetostriction in Fe and change the sign of the discontinuity of ${\alpha }_e$ at $T_C$ in Ni: the results differ qualitatively from those of the static approximation.