As a quantum mechanical function describes all the information about the system. We can solve the Schrodinger wave equation for a 2- body system or hydrogen atom to determine the allowed energy states of the system by knowing its wave function, but it is not possible to solve the Schrodinger wave equation for a N- body system. So the ultimate solution for this is the DFT. In the present work, the linear combinational of atomic orbital method as embodied in CRYSTAL code have been used to investigate the phase transition in technologically important compound CaO. The correlation and exchange scheme of PBE and Becke is used for building the Kohn-Sham Hamiltonian.