The assumption Murnaghan is to assume that the bulk modulus is a linear function of pressure: K = K 0 + P K 0 ′ Murnaghan equation is the result of the integration of the differential equation: P ( V ) = K 0 K 0 ′ [ ( V V 0 ) − − K 0 ′ − − 1 ] We can also express the volume depending on the pressure: V ( P ) = V 0 [ 1 + P ( K 0 ′ K 0 ) ] − − 1 / K 0 ′