Abstract:
Expressions for the anharmonic Helmholtz free
energy contributions up to o( f ) ,valid for all temperatures,
have been obtained using perturbation theory
for a c r ystal in which every atom is on a site of
inversion symmetry. Numerical calculations have been
carried out in the high temperature limit and in the
non-leading term approximation for a monatomic facecentred
cubic crystal with nearest neighbour c entralforce
interactions. The numbers obtained were seen to
vary by a s much as 47% from thos e obtai.ned in the
leading term approximati.on,indicating that the latter
approximati on is not in general very good. The convergence
to oct) of the perturbation series in the high
temperature limit appears satisfactory.
