From owner-chemistry@ccl.net Mon Jun  8 06:51:00 2020
From: "Thomas Manz thomasamanz[-]gmail.com" <owner-chemistry*_*server.ccl.net>
To: CCL
Subject: CCL: What is the electron density for double-hybrid functionals?
Message-Id: <-54088-200608064353-22999-XaFf6Z8WQoRk3hqJkLYt4w*_*server.ccl.net>
X-Original-From: Thomas Manz <thomasamanz%a%gmail.com>
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Date: Mon, 8 Jun 2020 04:43:34 -0600
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Sent to CCL by: Thomas Manz [thomasamanz[a]gmail.com]
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Dear colleagues,

I have a technical question about how the electron density is defined for
double hybrid functionals.

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 electron 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

(1) The Kohn-Sham electron density ansatz in which the electron density is
computed as Sum[(occupancy)(KSOrbital*)(KSOrbital)].

or

(2) The perturbation theory electron density ansatz in which a MP2-like
correction/contribution 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
contribution 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 using a completely different scheme that
does not employ a MP2-like energy correction. Do these double hybrids have
any special considerations when computing the electron density?

Sincerely,

Tom

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<div dir=3D"ltr">Dear colleagues,<div><br></div><div>I have a technical que=
stion about how the electron density is defined for double hybrid functiona=
ls.</div><div><br></div><div>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&#39;s energy and its elect=
ron density; in this case, a MP2 correction/contribution to both the energy=
 and electron density are computed.</div><div><br></div><div>My question is=
 therefore whether double-hybrid functionals are normally defined using=C2=
=A0</div><div><br></div><div>(1) The Kohn-Sham electron density ansatz in w=
hich the electron density is computed as Sum[(occupancy)(KSOrbital*)(KSOrbi=
tal)].</div><div><br></div><div>or</div><div><br></div><div>(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).</div><div><br></div>=
<div>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)?</div><div><br></div><div>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?</div><div><br></div><div>Sincerely,</div><div><br=
></div><div>Tom</div><div><br></div><div><br></div></div>

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