[Pw_forum] spin polarization of a organo-metallic compound

[Jia Chen]

Dear Giuseppe Mattioli,

It is quite surprising for me, that hybrid functional actually
overestimates stability of low-spin solution. I know a compound ,for
which, hybrid functional overestimates stability of high-spin solution. Do
you know any published papers with examples of hybrid functional favours
low-spin? Thank you very much!

Bests
Jia


On Fri, Jan 3, 2014 at 2:13 PM, Giuseppe Mattioli <
giuseppe.mattioli at ism.cnr.it> wrote:

>
> Dear Alex
> Paolo is right, of course. Check the convergence on the Re PP first.
> I would add a few words anyway. Hybrid DFT/HF functionals like B3LYP
> are pretty useful, but in the case of open-shell systems there are
> some known limitations. See the very interesting paper by Cohen
> (Science Vol. 321 no. 5890 pp. 792-794). The HF exchange term added to
> the DFT xc kernel leads to an overcoupling of electron pairs and,
> therefore, to an overestimate of the stability of low-spin solutions.
> Chemists usually call it a "static correlation" error. As we could
> spend years in discussing such an issue, I feel to suggest two simple
> tests: try to perform a B2PLYP calculation (if you can afford it) with
> your GTO package. The MP2 treatment of B3LYP correlation is supposed
> to correct part of the static correlation error. Otherwise, try to
> perform a DFT+U calculation with the U correction applied (possibly in
> a self-consistent fashion, see the many related papers by Cococcioni,
> De Gironcoli, Kulik, Marzari, and mine) to the Re 5d shell (I did
> never use Re... Are the 4f electrons embedded in the pseudo?). The
> on-site DFT+U method is supposed to be free from sce, or, better, less
> affected than its parent DFT functional. If you obtain a high-spin
> solution with one of these methods, there are sound reasons, in my
> opinion, to trust that it is a stable solution...
> HTH
> Giuseppe
>
> Giuseppe Mattioli
> ISM-CNR
> Italy
>
> Quoting Alex Granov <alex.granov at outlook.com>:
>
> > Hi
> > We are studying an organo-metallic compound which contains 3 Benzene
> > rings, phosphorous, oxygen, Iodine, and rhenium atoms.Our quantum
> > chemistry study using B3LYP/6-31+G* (Gaussian basis set) shows that
> > the ground state of the system is singlet (spin -unpolarized). We
> > attempted to optimize this structure using quantum espresso to
> > calculate some other electronic properties. Then surprisingly we
> > found that the spin-polarized system is more stable than the
> > spin-unpolarized one in contrast with our quantum chemistry study.
> > In the following you can see my input file and I wonder whether
> > there is something wrong in the input that made the very noticeable
> > contrast. I appreciate your comments to understand the issue and
> > solve it in advance.
> > q/e input:&control    calculation='relax',
> > restart_mode='from_scratch',    prefix='Re-Be',    pseudo_dir =
> > './pseudo/',    outdir='./tmp/',    tprnfor=.t. ,
> > etot_conv_thr=1.0D-4,    forc_conv_thr=1.0D-3,    nstep=300,
> > dt=10,     / &system    ibrav= 8, a=20, b=20, c=20,  nat=37, ntyp=6,
> >    ecutwfc = 30, ecutrho = 300, occupations='smearing',
> > smearing='marzari-vanderbilt', degauss=0.005,    nspin=2 ,
> > starting_magnetization(1)=1 ,starting_magnetization(2)=1 ,
> > starting_magnetization(3)=1 , starting_magnetization(4)=1 ,
> > starting_magnetization(5)=1 , starting_magnetization(6)=1 , /
> > &electrons    conv_thr = 1.0d-6,    mixing_beta=0.2,
> > mixing_mode=local-TF, / &IONS  ion_dynamics="bfgs",  upscale=100.0D0
> > ,/ATOMIC_SPECIESRe 186.207  Re.pbe-hgh.UPFO  15.999
> > O.pbe-rrkjus.UPFC 12.000    C.pbe-rrkjus.UPFH 1.000
> > H.pbe-rrkjus.UPFI 126.90   I.pbe-n-rrkjus_psl.0.2.UPFP  30.9737
> > P.pbe-n-van.UPFK_POINTS {gamma}
> >
> > -------------------------------------------------Alex
> > GranovМосковский физико-технический институт (MIPT)Moscow, Russia
>
>
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>     Giuseppe Mattioli
>     CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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-- 
Jia Chen
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