[Pw_forum] CuO, LDA+U, Pseudopots, etc.
Paul M. Grant
w2agz at pacbell.net
Fri Dec 14 08:20:27 CET 2007
To All responding to my initial thread:
I'm amazed and encouraged by the response of the community to my problem. I
will be trying your suggestions...e.g., a "rich man's" Wannier projection.
Of course, this trapping into a "metastable state" is typical of many highly
nonlinear systems of any type...such as the many body nonlinear
Navier-Stokes equations, sometimes referred to as the "weather."
Someone pointed out the importance of covalency in the Cu-O double bond, and
I'm not sure how to accommodate this in PWscf (in the simple Hubbard
Hamiltonian, you just futz around with U and t in a Monte Carlo
simulation...in 1 or 2 dimensions). As I mentioned in my original posting,
there may be a profound issue here that DFT LDA+U may find difficult to
address...it's probably the origin of HTSC. There is a polemic published
back in 1989 by Phil Anderson to the effect that pseudopotential theory may
not apply to divalent Cu-O bonds.
Nonetheless, I would still like to find a way to get a Hubbard Gap in
divalent CuO from a PW/PP starting point. I'm old enough to remember this
was once quite a task for NiO.
Paul M. Grant, PhD
Principal, W2AGZ Technologies
Visiting Scholar, Applied Physics, Stanford University
EPRI Science Fellow (Retired)
IBM Research Staff Member Emeritus
w2agz at pacbell.net
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
Behalf Of Agostino Migliore
Sent: Thursday, December 13, 2007 10:01 PM
To: PWSCF Forum
Subject: Re: [Pw_forum] CuO, LDA+U, Pseudopots, etc.
Yes, I know. By saying "convergence problem" I just meant, in this
specific case, that the scf calculation does not reach the right minimum
(i.e., the lowest one), but get trapped into some another (local) minimum.
As to your second point, I will send you a further email in a short time.
> Dear Agostino,
> if the calculation did converge to a local minimum, it means that the
> system has more than one minimum, not that there is a convergence
> problem (of course, the convergence strategy you choose will affect
> the minimum in which you fall).
> It would be very interesting to know more (when you have time) about
> these minima - e.g. what were the projections of the minority spin
> in the two cases.
> Thanks !
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