[gpaw-users] Error estimations for different XCs

[Wellendorff, Jess]

Hi wei.

That function should be in "gpaw/aseinterface.py" in the GPAW trunk.
I am sorry if the bee code in ASE trunk uses code not available in any GPAW stable version, but I have done it this way in order for ASE calculator interfaces with a "get_nonselfconsistent_energies" method to be equally able to get/return the BEE ensembles.

Best
Jess

On Sep 10, 2013, at 3:40 PM, wei guo wrote:

Thanks guys,

I see that get_xc_difference() is the method doing non-selfconsistently.
Or I can use the BEEF-vdw

When I try the example here, https://wiki.fysik.dtu.dk/gpaw/documentation/xc/vdw.html
I got a error when running de_h2 = ens.get_ensemble_energies()
It said
BEEF-vdW ensemble started
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/shared/ase/3.7.1.3184/ase/dft/bee.py", line 41, in get_ensemble_energies
    self.contribs = self.calc.get_nonselfconsistent_energies(self.beef_type)
AttributeError: GPAW instance has no attribute 'get_nonselfconsistent_energies'

Jess, did I miss some modules？
Thanks



On Tue, Sep 10, 2013 at 3:37 AM, Jens Jørgen Mortensen <jensj at fysik.dtu.dk<mailto:jensj at fysik.dtu.dk>> wrote:
Den 10-09-2013 01:58, Wellendorff, Jess skrev:
Dear Wei,

a much more systematic approach to your quest is to use the BEEF-vdW functional with the corresponding Bayesian Error Estimation Ensemble.
This ensemble actually does exactly what you are looking for without the need for you to specify which "standard functionals" define the spread of DFT results. Instead, the error estimate (or estimate of the spread of predictions by different density functionals) is calculated simply as the square root of the variance over the BEEF-vdW ensemble predictions. Search for "BEEF-vdW" on the GPAW web pages.

I really recommend this approach. It gives you a much less biased and more quantitative estimate of the sensitivity of your DFT result wrt the density functional you have chosen. Think about the inherent bias in this way: How can you be sure that you know by heart the two density functionals that would provide predictions at the two ends of the true distribution of DFT predictions of the quantity you are interested in ??? That is very hard, if not impossible. But the BEE approach offers a convenient and cheap estimate of how much your DFT prediction would change had you chosen other XC functionals than the BEEF-vdW one (provided the quantity of interest is posed in terms of total energies).

Here is a simple example showing how to calculate the energy for another functional non-selfconsistentily (look at the PBE.py file):

  https://wiki.fysik.dtu.dk/gpaw/exercises/iron/iron.html

Jens Jørgen


Best
Jess Wellendorff

On Sep 9, 2013, at 11:49 PM, Glen Jenness wrote:

Dear Wei,

Off the top of my head you can do something like :

calc = GPAW(....)

potentials = ['PBE', 'LDA', 'PW91']

for xc in potentials:
    calc.set(xc=xc)
    <calculate binding energy here>

This will actually work with most of the ASE calculators.

Glen




On Mon, Sep 9, 2013 at 5:18 PM, wei guo <guoweicyclone at gmail.com<mailto:guoweicyclone at gmail.com>> wrote:
Hi guys,

We are interested in calculate the binding energies using different XC to get a sense how the errors are related to XCs.

To save time, I guess one can start from the relaxed structure and in one calculation obtain all the potential energies of a few XCs.

Is there any function or module in GPAW or ASE for doing this

Thanks.
--
Best wishes
Wei
----------------------------------------------------------------
353 Colburn Lab
Center for Catalytic Science and Technology
Department of Chemical Engineering
University of Delaware
Newark, DE 19716-3111
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--
Dr. Glen Jenness
Schmidt Group/Morgan Group
Department of Chemistry/Materials Science and Engineering (MSAE)
University of Wisconsin - Madison
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Dr. Jess Wellendorff
Postdoctoral Researcher
SUNCAT Center for Interface Science & Catalysis
SLAC National Accelerator Laboratory, U.S.A.
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--
Best wishes
Wei
----------------------------------------------------------------
353 Colburn Lab
Center for Catalytic Science and Technology
Department of Chemical Engineering
University of Delaware
Newark, DE 19716-3111
Tel:(302)-831-1132
----------------------------------------------------------------

-----------------------------------------------------------------------
Dr. Jess Wellendorff
Postdoctoral Researcher
SUNCAT Center for Interface Science & Catalysis
SLAC National Accelerator Laboratory, U.S.A.
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