[Pw_forum] question on electron_dynamics and orthogonalization

Nicola Marzari marzari at MIT.EDU
Wed Mar 29 22:49:05 CEST 2006

Hi Nichols,

what you are doing is extremely useful.

The two calculations seem actually in good agreement, but of
course beauty is in the eye of the beholder.

The total energies are within 1 mRy of each other, and the forces
seem to have a factor of 2 difference (that is correct - in PWSCF
the forces are in Ry/bohr, while in CP they are in Ha/bohr; PWSCF
labels the forces as  Ry/au, that is the same as saying Ry/bohr,
and CP says that they are in atomic units, and atomic units for the
forces are Ha/bohr).

The eigenvalues are different, but as long as it's a rigid shift between
the two, we are fine (the two codes have clearly a different measure of 
what is zero in the energy scale - maybe someone could comment on this).

The stresses are wildly different, but this is a bug we also noticed a
week ago, and Paolo Giannozzi and Carlo Cavazzoni are tracking it down.
Bug in CP.

Let us know - if you want an ultimate comparison, try to run both in 
serial, make sure that the fft grids are the same (they are, in your
case, 40 45 64), tighten the tolerance on the energy convergence as much
as possible, and see what you get - it helps having an unrelaxed, out
of equilibrium structure, so you get forces that are fairly large.

But the agreement between the codes seems actually very good, at this
stage - a part from the stress.

Let us know if you find something else that I might have missed.



Nichols A. Romero wrote:

> Nicola (or anyone else on this list),
> I am going to ask a question that get's asked on this list very
> frequently (possibly second only to "Why doesn't the code compile?").
> I am struggling with trying to get PWSCF and the CP code to agree. I
> am sure the PWSCF is correct, but I don't know about the CP
> calculation. All I want to immediately do with the CP is to calculate
> the ground state and have it agree with PWSCF. Though the next step is
> to do BO MD with the CP code (which I remember correctly, is still in
> the testing phase).
> I'm attaching a model problem I've been playing with for the last two
> days. I include the input and outputfiles. The US_PP are of the PBE
> RRKJ type that are found on the PWSCF website. It should run fairly
> quickly on a desktop computer.
> I would appreciate any help at this point. I'm sure that I am not
> understand the definition of some of the CP parameters. FYI, I am
> using the CVS version of Q-ESPRESSO as stated in my previous e-mail.
> Bests,
> On 3/28/06, Nicola Marzari <marzari at mit.edu> wrote:
>>I'll let Paolo or Kostya or Ismaila confirm, but my guess is that once
>>electron-dynamics is "cg" you want a gram-schmidt orthogonalization.
>>We might implement an iterative ortho sometimes in the future, but I
>>believe at this stage gram-schmidt is the only choice.
>>Note that the latest CVS (2-3 days ago) has a number of calbec calls
>>removed, and should be faster.
>>We are still optimizing the code, but it should be fairly robust at this
>>stage - let us know of any feedback you might have.
>>                                        nicola
>>Nichols A. Romero wrote:
>>>This is a question about CP code (i.e. not PWSCF). I am using the CVS version.
>>>Are the keywords
>>>electron_dynamics & orthogonolization
>>>completely independent of each other when
>>>electron_dynamics = 'cg'
>>>Forgive, my ignorance. I am mostly familiar with the PWSCF component
>>>of Q-Espresso.
>>>When doing an initial 'cg' calculation to get the groundstate on the
>>>BO surface, doesn't the 'cg' routines impose the orthonomality
>>>constraint automattically? Why does one need a seperate
>>>*orthogonalization* keyword? (which has two different options?)
>>>Nichols A. Romero, Ph.D.
>>>1613 Denise Dr. Apt. D
>>>Forest Hill, MD 21050
>>>443-567-8328 (C)
>>>410-306-0709 (O)
>>>Pw_forum mailing list
>>>Pw_forum at pwscf.org
>>Prof Nicola Marzari   Department of Materials Science and Engineering
>>13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
>>tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu
>>Pw_forum mailing list
>>Pw_forum at pwscf.org
> --
> Nichols A. Romero, Ph.D.
> 1613 Denise Dr. Apt. D
> Forest Hill, MD 21050
> 443-567-8328 (C)
> 410-306-0709 (O)

Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu

More information about the users mailing list