Ab initio calculation of the thermal properties of Cu: Performance of the LDA and GGA

The thermal properties of bulk copper are investigated by performing ab initio DFT and DFPT calculations and using the quasiharmonic approximation for the free energy. Using both the LDA and the GGA for the exchangecorrelation potential, we compute the temperature dependence of the lattice constant, coefficient of thermal expansion, bulk modulus, pressure derivative of the bulk modulus, phonon frequencies, Grüneisen 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/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/GGA errors should increase with temperature. PACS #: 63.20.Ry, 65.40.+g, 65.70.+y, 71.15.Mb