Fit to Murnaghan equation of state: f(x)=E0+K*V*( (1.0/(K2*(K2-1)))*(x/V)**(1.0-K2) + 1.0/K2*x/V - 1.0/(K2-1.0) )
where x is the volume, E0 and V0 are reference energies and volumes (at zero pressure),
and K is the bulk modulus at zero pressure and K' is the slope of the bulk modulus change with pressure.

K=    eV / A^3
K2=
V0=
E0=

from fitting E(V), with V in A^3 and E in eV.

Conversion between eV/A^3 and GPa is 16.0218 GPa / (eV/A^3)

K= GPa

