Birch-Murnaghan fitting

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In many cases, it might not be recommended to do a full geometry optimisation with VASP (ISIF = 3 in INCAR file). In these cases you can calculate the equilibrium lattice parameter at 0 K by doing a Birch-Murnaghan fit. More information about the Birch-Murnaghan equation, the fitting procedure and how to do the fit in practice are found in the pdf-file:

Description of the Birch-Murnaghan equation

For calculating the equilibrium lattice constant with the least squares method, you can use the libreoffice file, in which you only need to enter your calculation results. The fitting and calculation of the resulting equilibrium will be done automatically:

Automatic calculation of the lattice parameter with Libreoffice

In the Libreoffice document there is also a 2nd sheet with an example calculation.