Hallo, If I dare to add my two cents to the discussion, Ruslan's volume as calculated by hand (for the Murnaghan fit) is A^3 whereas the unit cell volume (per which the energy is calculated) is A^3/4, as for fcc structure. Whereas for a reasonable fit, the volume and the energy should be compatible.
By the way you don't need to calculate volume by hand, it suffices do uncomment, or modify, one of the commands which transform the read data (e.g., your lattice constant) into whatever you need (e.g., correct volume) Good luck Andrei Postnikov > Dear Siesta users, > > can you please help me with with Postnikov's tool: Murnaghan equation of > state fit. > > LatticeConstant 6.12 Ang > %block LatticeVectors > 0.000 0.500 0.500 > 0.500 0.000 0.500 > 0.500 0.500 0.000 > %endblock LatticeVectors > NumberOfAtoms 2 > NumberOfSpecies 2 > %block ChemicalSpeciesLabel > 1 31 Ga-3d > 2 51 Sb > %endblock ChemicalSpeciesLabel > AtomicCoordinatesFormat ScaledCartesian > %block AtomicCoordinatesAndAtomicSpecies > 0.000 0.000 0.000 1 # Ga 1 > 0.250 0.250 0.250 2 # Sb 2 > %endblock AtomicCoordinatesAndAtomicSpecies > > The generated values are: > > alat (Ang) Etot (eV) > ------------------------------ > 6.12 -1975.526018 > 6.14 -1975.531451 > 6.16 -1975.535169 > 6.18 -1975.53714 > 6.20 -1975.537384 > 6.22 -1975.535722 > 6.24 -1975.5324 > 6.26 -1975.527514 > > > Then I translated Ang units to atomic units and eV to Rydbergs as > requested > by Postnikov's tool: Murnaghan equation of state. Then set Volume=alat^3. > > The output from this tool contains: > > # Equilibrium volume, a.u.^3 : 602.102908 > # Minimum energy, Ry : -145.201385 > # Bulk modulus, Kbar : 47.134730 > > The values are seriously wrong since for GaSb > GaSb zincblende a=6.09593 Ang, B=57.0 GPa > > > What I am doing wrong? > > > Ruslan >
