Experimental data on the vacancy concentration in metals, when shown in an
Arrhenius plot, give an approximate straight line as a function of 1/T but
often with a slight upward curvature close to the melting point T-m. This f
eature has usually been attributed to a divacancy contribution. We have per
formed molecular dynamics simulations on copper, using a slightly modified
model potential due to Cleri and Rosato (Ref. 7). Our results show that div
acancy effects are negligible, but that there is an important contribution
from anharmonicity in the lattice vibrations, giving rise to the curvature
in the Arrhenius plot. As a consequence, one must apply significant correct
ions to the vacancy formation enthalpy and entropy before they are compared
with theoretical values that usually refer to zero kelvin and harmonic vib
rations, respectively.