Results of the ab *initio* molecular dynamics calculations of
silicon crystals are presented by means of analysis of the velocity
autocorrelation function and determination of mean phonon relaxation
time. The mean phonon relaxation time is crucial for prediction of the
phonon-associated coefficient of thermal conductivity of materials. A
clear correlation between the velocity autocorrelation function
relaxation time and the coefficient of thermal diffusivity has been
found. The analysis of the results obtained has indicated a decrease of
the velocity autocorrelation function relaxation time t with increase of
temperature. The method proposed may be used to estimate the coefficient
of ther-mal diffusivity and thermal conductivity of the materials based
on silicon and of other wide-bandgap semiconductors. The correlation
between kinetic energy fluctuations and relaxation time of the velocity
autocorrelation function has been calculated with the relatively high
coefficient of determination R2 = 0.9396. The
correlation obtained and the corresponding approach substantiate the use
of kinetic energy fluctuations for the calculation of values related to
heat conductivity in silicon-based semiconductors (coefficients of
thermal conductivity and diffusivity).