Article

# Phonon spectrum, thermal expansion and heat capacity of UO$_2$ from first-principles

10/2011;
Source: arXiv

ABSTRACT We report first-principles calculations of the phonon dispersion spectrum,
thermal expansion, and heat capacity of uranium dioxide. The so-called direct
method, based on the quasiharmonic approximation, is used to calculate the
phonon frequencies within a density functional framework for the electronic
structure. The phonon dispersions calculated at the theoretical equilibrium
volume agree well with experimental dispersions. The computed phonon density of
states (DOS) compare reasonably well with measurement data, as do also the
calculated frequencies of the Raman and infrared active modes including the
LO/TO splitting. To study the pressure dependence of the phonon frequencies we
calculate phonon dispersions for several lattice constants. Our computed phonon
spectra demonstrate the opening of a gap between the optical and acoustic modes
induced by pressure. Taking into account the phonon contribution to the total
free energy of UO$_2$ its thermal expansion coefficient and heat capacity have
been {\it ab initio} computed. Both quantities are in good agreement with
available experimental data for temperatures up to about 500 K.

0 0
·
0 Bookmarks
·
55 Views

Available from
4 Mar 2013

### Keywords

available experimental data

calculate phonon dispersions

computed phonon density

density functional framework

experimental dispersions

good agreement

heat capacity

infrared active modes

lattice constants

LO/TO splitting

measurement data

optical

phonon contribution

phonon dispersion spectrum

phonon dispersions

phonon frequencies

pressure dependence

thermal expansion

thermal expansion coefficient

{\it ab initio} computed