[Pw_forum] Display of forces in a pure scf run

[Cristian Degli Esposti Boschi]

Dear Stefano and Axel, thanks for your replies. Actually question can be 
rephrased as follows. Thanks to the Hellmann-Feynman theorem
in order to compute the ionic forces I need only the partial
derivatives of the total energy with respect to the ionic coordinates
(see for instance 7.5 and 7.8 in Payne et al., RMP 64, p. 1045).
If no real displacements of the atoms are needed to compute
these derivatives, then I guess that they can be simply calculated
as expectation values of the Hamiltonian on the current wavefunction
because they can written down once a (parametrized) expression of the
ionic potential is chosen. Am I right?

Thanks for still devoting time to this...

-- 
Cristian Degli Esposti Boschi
CNR-IMM, Sezione di Bologna,
via Gobetti, 101, 40129, Bologna, Italia
tel. ++39 051 6399152, fax ++39 051 6399216
degliesposti -AT- bo.imm.cnr.it