Path-integral Monte Carlo calculation of the effects of thermal disorder in extended x-ray-absorption fine structure of copper

The distributions of interatomic distances of the first four coordination shells of copper and their leading cumulants have been determined by a path-integral Monte Carlo calculation on a many-body potential model, in the temperature range of 4-300 K. The asymmetry of the distance distribution, measured by the third cumulant, is much larger for the first shell than for the outer shells. The mean value of the distance between neighboring atoms is given for each shell by the first cumulant of the distribution. This allowed us to test a well-known method of estimating the thermal expansion of each shell from the second and third cumulants of its distribution. This method gave values smaller by 40% for the first shell and much smaller for all outer shells.