[Pw_forum] spin polarization of a organo-metallic compound

[Giuseppe Mattioli]

Dear Alex
I note that the energy difference between spin-polarized and diamagnetic ground states in the B2PLYP calculations is much lower than in B3LYP, so my 
previous guess was not totally wrong. This is reassuring...:-) 
I can suggest some further checks on your last results before admitting (and it may still be possible... :-( ) that GTO and PW results are 
intrinsically incommensurable. I'm not familiar with Firefly, and I'm not sure if what I suggest can be actually done, so I apologize in advance...

a) If I understand and remember well you have performed your plane wave calculations with QE by using a "plain vanilla" PBE functional (no exx, no 
dft+u, no dispersion correction) Could you perform the same PBE calculation with Firefly? If the GTO results are similar to the PW ones the differences 
are not due to the basis sets but to the xc functionals.

b) I do not know your system, nor Firefly, so I cannot say for sure, but can you check if your GTO calculations include some dispersion correction 
(DFT-D3, usually) which may change the equilibrium geometry significantly wrt the PW case?

c) I see heavy elements in your molecule. Is there any trick which accounts for spin-orbit or relativistic contributions in your all-electron GTO 
calculations? If not, could you try to use some? I can suggest (if implemented) to try with effective core potentials (ECP. I've obtained good results 
with those contained here: http://www.theochem.uni-stuttgart.de/pseudopotentials/), which represent also the most similar setup to PW/pseudopotential 
calculations.

d) Did you push the ecutwfc/ecutrho limits further than 70/600 Ry in the PW calculations? I would suggest to reach at least 100/400 (yes, it is not a 
typo... 400 Ry on the electron density seem to be adequate for all of your US pseudopotentials, and NC pseudopotentials usually require a density 
cutoff not larger than 4*ecutwfc) and check the convergence of total energies.

e) There is no strict rule which forbids the use of US pseudopotentials together with NC ones, but if you pay the price (in terms of wfc cutoff) of the 
latter ones, you could try to use all NC... I've been comfortable since long with
O.pbe-mt.UPF
C.pbe-mt.UPF
H.pbe-vbc.UPF
which you should find in the online PP library.

HTH

Giuseppe


On Thursday 09 January 2014 07:11:56 Alex Granov wrote:
> Dear Giseppe
> Thank you very much for your kind attention and the details were said by
> you about spin polarization of such systems.I am sorry for the delay to
> reply your comments. I was doing what proposed by you and Stefano to see
> the difference origin. so in the following we can see the results
> obtained:
> Quantum -Espresso:
> ecutwfc = 70, ecutrho = 600,   (the cutoff has been increased as proposed
> by Stefano)Re 186.207  Re.pbe-mt_fhi.UPFO  15.999   O.pbe-rrkjus.UPFC
> 12.000    C.pbe-rrkjus.UPFH 1.000     H.pbe-rrkjus.UPFI 126.90  
> I.pbe-mt_fhi.UPFP  30.9737  P.pbe-mt_fhi.UPF E=  -312.61421481 Ry
> (spin-unpolarized)E=  -312.66455244 Ry (spin-polarized, total
> magnetization=4.00 Bohr mag/cell
> 
> Firefly (Quantum Chemistry Code):
> B3LYP/6-31++G**:P,C,O,H; LANL2DZ:Re,I  (the system optimized using this
> method) E (S=0) = -1202.07856 HartreeE (S=1) = -1202.06949 E (S=2) =
> -1202.04809 B2PLYP/6-31++G**:P,C,O,H; LANL2DZ:Re,I (the energy of previous
> step was modified by adding the MP2 part as proposed by Giseppe) E (S=0) =
> -1199.826275 HartreeE (S=1) = -1199.825679 E (S=2) = -1199.820273
> 
> As still could be seen the plane-wave calculation shows that the
> spin-polarized system is the ground state and quantum chemistry
> calculation using Gaussian-like basis sets shows the trend conversely.
> 
> -------------------------------------------------Alex GranovМосковский
> физико-технический институт (MIPT)Moscow, Russia


********************************************************
- Article premier - Les hommes naissent et demeurent
libres et ègaux en droits. Les distinctions sociales
ne peuvent être fondèes que sur l'utilitè commune
- Article 2 - Le but de toute association politique
est la conservation des droits naturels et 
imprescriptibles de l'homme. Ces droits sont la libertè,
la propriètè, la sùretè et la rèsistance à l'oppression.
********************************************************

   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
   v. Salaria Km 29,300 - C.P. 10                
   I 00015 - Monterotondo Stazione (RM)          
   Tel + 39 06 90672836 - Fax +39 06 90672316    
   E-mail: <giuseppe.mattioli at ism.cnr.it>
   ResearcherID: F-6308-2012
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140109/c6c253e3/attachment.html>