In my experience, very good bulk moduli are produced by a simple quartic fit to five points no far than 1% off the equilibrium, you don't actually need lots of points or the Murnaghan fit (as long as you keep your points close enough to the equilibrium value). Just run five calculations with fixed lattice constants. Though you should check for the discontinuities caused by a finite integration grid (MeshCutoff). It is also very important which material you are studying, for example you shouldn't expect good results with molecular crystals like fullerite. Could you please specify the material?
2007/3/1, Oleksandr Voznyy <[EMAIL PROTECTED]>:
Do you have a cubic cell? Don't do VariableCell then, it destroys symmetry. (check the forces on atoms to be 0) If you know the exact symmetry of the cell (relative positions of atoms in the cell) then adjust only lattice constant. Then the effect of pressure in all direction will change the lattice equivalently as well. With the same relative coordinates just change the lattice constant in the range +-3% with the step 0.25-0.5% and check the total energies.
