[Pw_forum] fluctuation in SCF energies of CO adsorbed on Pd110

[David Foster]

Thanks Axel
Yes, in chemistry wee see always the MOs. But in many unknown cases, we should calculate the MOs by computations. To use the codes, we need to define 2S+1. In quantum chemistry codes we use different spin-multiplicity, and we choose each one that give smaller energy. What about plane-wave methods? 
Why choosing spin-polarization causes that the energy fluctuate so much?
If I compare these two calculations (one with spin-polarization and one without it), I should get the same energy. Is it right?

Thanks again
Any help will be appreciated. 

Regards

David Foster

Ph.D. Student of Chemistry

--------------------------------------------
On Mon, 4/21/14, Axel Kohlmeyer <akohlmey at gmail.com> wrote:

 Subject: Re: [Pw_forum] fluctuation in SCF energies of CO adsorbed on Pd110
 To: "PWSCF Forum" <pw_forum at pwscf.org>
 Date: Monday, April 21, 2014, 1:17 AM
 
 On Mon, Apr 21, 2014 at 12:03 AM,
 David Foster <davidfoster751 at yahoo.com>
 wrote:
 > Dear Yun
 > Thanks for your rapid answer. Considering your answer,
 I have two more questions:
 >
 > 1- In the system I have carbon monoxide. carbon atom
 has 4 electron in its valance. between O and C there is a
 triple bond. So, carbon may have one unpaired electron that
 needs spin-polarization defined. Is it right?
 
 wrong. electrons cannot be "assigned" to individual atoms,
 they occupy
 "molecular" orbitals. please help yourself to a little
 quantum
 chemistry refresher.
 
 > 2- Surface of metals due to the charge density near to
 the surface needs spin-polarization. Is it right?
 
 wrong. you need spin polarization only if you have unpaired
 electrons..
 
 > One more point. I have prepared input with one
 graphical program. When I see the input file with XCrysDen,
 in the primitive form everything is OK, but in conventional
 form, three to four Pd atoms in the edge of cell seems to be
 missing!!!!
 
 that is just visualization. probably your initial geometry
 has some
 rounding errors in the positions.
 
 axel.
 
 > Regards
 >
 > David Foster
 >
 > Ph.D. Student of Chemistry
 >
 > --------------------------------------------
 > On Sun, 4/20/14, Yun Wang <yun.wang at griffith.edu.au>
 wrote:
 >
 >  Subject: Re: [Pw_forum] fluctuation in SCF
 energies of CO adsorbed on Pd110
 >  To: "PWSCF Forum" <pw_forum at pwscf.org>
 >  Date: Sunday, April 20, 2014, 2:41 PM
 >
 >  Hi David,I think
 >  you need not consider the spin polarization for
 this system,
 >  which will accelerate the
 >  convergancy.Cheers,Yun
 >
 >
 >
 >
 >
 >  On Mon, Apr 21, 2014
 >  at 2:20 AM, David Foster <davidfoster751 at yahoo.com>
 >  wrote:
 >
 >
 >  Dear users
 >
 >
 >
 >  I have prepared an input for interaction between
 CO and
 >  Pd(110). I optimized 3*3*3 supercell of Pd bulk,
 and then
 >  cleaved a 110 surface and constructed a slab. I
 inserted CO
 >  molecule which has been optimized with QE5.0.2 in
 it. Now, I
 >  try to optimize this mixed system (CO+Pd(110)).
 >
 >
 >
 >
 >
 >  My main problem is that in scf I see the
 fluctuation in
 >  energies. My input and output has been attached.
 In all
 >  calculations I used QE5.0.2 and the same USPP. I
 used PBE
 >  DFT in the PP. I used nspin=2 due to the presence
 of oxygen
 >  atom. I introduced start_magnetization for all
 species. I
 >  fixed three bottom layers in the cell. I used
 ibrav=14 to
 >  optimize bulk phase of Pd, and didn't change it
 in all
 >  computation.
 >
 >
 >
 >  I used degauss=0.001RY. In addition I used
 smearing
 >  technique for both bulk and slab.
 >
 >
 >
 >  The run is continuing, but I think finally, I
 will encounter
 >  with problem.
 >
 >
 >
 >  Any idea for rapid convergence and solve the
 issue in
 >  fluctuation energy is appreciated.
 >
 >
 >
 >
 >
 >
 >
 >
 >
 >  Regards
 >
 >
 >
 >  David Foster
 >
 >
 >
 >  Ph.D. Student of Chemistry
 >  _______________________________________________
 >
 >  Pw_forum mailing list
 >
 >  Pw_forum at pwscf.org
 >
 >  http://pwscf.org/mailman/listinfo/pw_forum
 >
 >
 >
 >  --
 >
 >  Dr. Yun Wang
 >  Research Fellow
 >  Centre for Clean Environment and Energy
 >  Griffith School of Environment
 >  Gold Coast Campus, Griffith University
 >  QLD 4222, Australia
 >  Tel:(61-7) 5552 8456
 >  Fax:(61-7) 5552 8067
 >
 >
 >
 >
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 -- 
 Dr. Axel Kohlmeyer  akohlmey at gmail.com 
 http://goo.gl/1wk0
 College of Science & Technology, Temple University,
 Philadelphia PA, USA
 International Centre for Theoretical Physics, Trieste.
 Italy.
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