Hard-Sphere variational approach using an ab initio molecular dynamics code

We present a variational method to determine the total free energy of the electron and ion system by using the Gibbs-Bogolyubov inequality and a hard-sphere reference system applied to the ab initio molecular dynamics code CPMD. Electrical conductivity and transport coefficients are calculated. Numerical results and comparisons with quantum molecular dynamics simulations and experiments are presented and discussed for dense and expanded aluminum. The variational approach using the ab initio molecular dynamics code CPMD is more than ten times faster than CPMD simulations.