[Pw_forum] calculating the stress tensor

[Nichols A. Romero]

Hi,

I and another post-doc are working on implementing a non-local
functional into PWSCF. It is of the general form:
E_xc[n(r)] = \int dr dr' n(r) phi(r,r') n(r')

where n(r) and phi(r,r') are the charge density and a kernel, respectively.

Forces require calculating V_xc which is analytically complicated, but
has already been done. The next quantity that we want to compute is
the stress tensor.

Does any happen to have any notes on calculating the stress tensor in
a PW basis set?

I looked at the original paper on calculating the stress:

O. H. Nielsen and R. M. Martin, Phys. Rev. Lett. 50, 697 (1983).

Eqn. 3 contains the V_xc (mu_xc in their notation) and it also
contains epsilon_xc which is the exchange-correlation energy per
particle which cannot be easily written down in a closed analytic form
for a non-local functional (I think). Otherwise, I don't see any
higher derivatives of E_xc in the the expression for the stress.

Does anyone have any useful references?

Thanks,
-- 
Nichols A. Romero, Ph.D.
1613 Denise Dr. Apt. D
Forest Hill, MD 21050
443-567-8328 (C)
410-306-0709 (O)