Role of ab initio calculations in high pressure-high temperature studies and material properties

We present the results of our studies using the first principles theories on materials in which controversies exist in the diamond anvil cell based high pressure data. The importance of theoretical simulations based on the first principles molecular dynamics or based on embedded atom potentials to study the dynamic response of condensed matter under shock is highlighted with results and their comparison with experimental data of time dependent X-ray diffraction. Finally, realizing the inadequacy of many variants of Thomas-Fermi-Dirac theories to simulate the matter in 10 to few hundred Mbar pressures, there is need to treat the LDA or GGA theories with due consideration of the core states becoming delocalized under these extreme pressures as a result of pressure and thermal ionization