In some circumstances, particularly in connection with ab initio calculations, the expression of the energy as a function of the volume will be preferred, which can be obtained by integrating the above equation according to the relationship P = − dE / dV. It can be written to K ′ 0 different from 3, E ( V ) = E 0 + K 0 V 0 [ 1 K 0 ′ ( K 0 ′ − − 1 ) ( V V 0 ) 1 − − K 0 ′ + 1 K 0 ′ V V 0 − − 1 K 0 ′ − − 1 ] .