Ab initiocalculation of the thermal properties of Cu: Performance of the LDA and GGA

The thermal properties of bulk copper are investigated by performing ab initio density functional theory and density functional perturbation theory calculations and using the quasiharmonic approximation for the free energy. Using both the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation potential, we compute the temperature dependence of the lattice constant, coefficient of thermal expansion, bulk modulus, pressure derivative of the bulk modulus, phonon frequencies, Gr\"uneisen parameters, and the electronic and phonon contributions to the specific heats at constant volume and constant pressure. We obtain answers in closer agreement with experiment than those obtained from more approximate earlier treatments. The LDA and GGA errors in computing anharmonic quantities are significantly smaller than those in harmonic quantities. We argue that this should be a general feature and also argue that LDA and GGA errors should increase with temperature.