Solution LAB1 diamond bulk modulus

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Bulk modulus of diamond

Using the data produced in the previous exercise (total energy as a function of the lattice parameter for a range of ecutwfc values), one can do the following:

• extract etot vs volume for each wfcutfc value into different files;
• fit the data and extract the second derivative in the minimum;
• this can be done using a second (or better higher) order polynomial or other fitting functions (cubic splines, Murnaghan equation of state, ...)
• Evaluate the bulk modulus taking care of unit conversion to international system (B modulus is given in GPa)
• The above steps are coded in the script ./LabQSM/tools/compute_B_modulus.py for convenience

Results as a function of the kinetic energy cutoff follow.