WIEN2k-FAQ: How to calculate atomization and cohesive energies?

©2001 by P. Blaha, K. Schwarz and J. Luitz

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The atomization energy or cohesive energy of a compound AxBy is the difference between the energy of the crystal and the energies of the free atoms:

Eatomization = Ecrystal - x * EA - y * EB

The atomic energies for elements lighter than Ne can probably be taken from case.outputst. However, for heavier atoms, due to the scalar relativistic approximation one must do an "equivalent" atomic calculation, otherwise you can get even "positive" atomization energies (compound is unstable).

PS: Of course you must use identical EXC and other (non-default) computational parameters !!!
PPS: In case the scf stops with QTL-B error in the very first cycle, it probably comes because in an atom EF is usually a negative number. Modify case.in1 and put eg. -0.5 as EF in case.in1.
PPPS: Since for such "empty" cells EF will be most likely at negative energies (eg. -0.3 or similar), you may have to adjust the energy parameters in case.in1. Once the scf-cycle has finished, you may need to readjust these energy parameters by hand (compare eigenvalues, fermi energy and :EP labels from your scf file).

The formation energy (at T=0 K) of a compound AxBy is the difference between the energies of this crystal and the stable phases of the elements:

Ecohesive = Ecrystal - x * EA - y * EB

If A is eg. Fe, do a bcc Fe calculation (including Vol-optimization) for EA, and so on for other elements.
If B is oxygen (hydrogen, nitrogen,...), one usually takes the O2 molecule as reference. This leads to a bit cumbersome and expensive procedure:

Peter Blaha,