Dear colleagues,

=

--0000000000000a326d05a79049d3--
I have a technical que=
stion about how the electron density is defined for double hybrid functiona=
ls.

Some double hybrid functionals use a MP2-like =
contribution to the energy. In standard (non-DFT) MP2 calculations, the MP2=
perturbative correction affects both the system's energy and its elect=
ron density; in this case, a MP2 correction/contribution to both the energy=
and electron density are computed.

My question is=
therefore whether double-hybrid functionals are normally defined using=C2=
=A0

(1) The Kohn-Sham electron density ansatz in w=
hich the electron density is computed as Sum[(occupancy)(KSOrbital*)(KSOrbi=
tal)].

or

(2) The perturb=
ation theory electron density ansatz in which a MP2-like correction/contrib=
ution to the electron density is included (using the appropriate weight of =
MP2-like correlation in the double-hybrid functional).

Do all double hybrid functionals that include a MP2-like energy contri=
bution currently define the electron density in the same way (either (1) or=
(2)) or do some define the electron density using (1) while others define =
it using (2)?

Some double-hybrids are defined usin=
g a completely different scheme that does not employ a MP2-like energy corr=
ection. Do these double hybrids have any special considerations when comput=
ing the electron density?

Sincerely,

Tom