[Pw_forum] spin polarization of a organo-metallic compound
Giuseppe Mattioli
giuseppe.mattioli at ism.cnr.it
Sat Jan 4 00:12:22 CET 2014
Dear Jia
One last (at least for now...) word, which perhaps deserves to be
written. Let us focus on excess electrons in transition metal oxides
(only because I've studied them for long). If you create an O vacancy
in Ti(IV)O2 the missing O atom lets back two excess electrons. If you
perform a conventional DFT (i.e., PBE) calculation the two excess
electrons are delocalized in the conduction band and the total
magnetization is 0 muB. Here the delocalization (self interaction,
double counting, ...) error spread "little pieces of electron" around
all the supercell. Both EXX and DFT+U methods localize the electrons
on two Ti(III) sites neighbouring the missing O because they tend to
linearize the E(N) vs N curve and, therefore, to create a (correct)
derivative discontinuity at integer N values in the E(N) curve. They
also can provide high-spin solutions, and in this regard you are
right: the correction of delocalization errors by EXX can provide high
spin results. Regarding the O vacancy, my DFT+U result is a supercell
with two unpaired electrons on the two Ti(III) sites. They can be
antiferromagnetically (S=1) or ferromagnetically (S=3) coupled,
slightly depending on U values, convergence, ...: in chemical language
they have therefore always the highest multiplicity of electrons, and
the high-spin and broken-symmetry solutions are very close in energy,
so close that I'm not really sure about the lowest one, because I've
not pushed down the forces on nuclei at very very low values. There
are several papers by Pacchioni, Di Valentin and Selloni where the O
vacancy has been investigated by using B3LYP in a periodic GTO
approach. Of course I've not got them here with me, but I (faintly)
remember that the low-spin solution (two electrons coupled on the same
Kohn-Sham orbital shared between the same two Ti(III) centers) was
competitive in energy with the open-shell one far more than in my
DFT+U calculations, and this fact involves the static correlation
problem discussed before. The differences between the DFT+U and B3LYP
total density distributions were minimal, so which is the "correct"
solution? In my opinion these problems are among the most interesting
challenges for dft, and I would be very glad to test some mp2 trick on
correlation like B2PLYP in plane wave calculations...
Sorry for the long answers, and Happy New Year to you!
G.
Giuseppe Mattioli
ISM-CNR
Italy
Quoting Jia Chen <jiachenchem at gmail.com>:
> Dear Giuseppe,
>
> It is very nice of you to provide so much information! It is certainly much
> more to this question than I thought earlier. Thank you very much and Happy
> New Year.
>
> Cheers
> Jia
>
>
> On Fri, Jan 3, 2014 at 4:27 PM, Giuseppe Mattioli <
> giuseppe.mattioli at ism.cnr.it> wrote:
>
>>
>> Dear Jia
>> Sorry, I'm not at my usual desktop, and I cannot therefore access to
>> the whole of my data base. But I can recall by heart this paper
>> Scherlis, Cococcioni, Sit and Marzari; J. Phys. Chem. B 2007, 111,
>> 7384-7391
>> which investigates the spin states of the well known iron(II)
>> porphyrin and of some of its (Fe(II) and Fe(III)) derivatives. In that
>> case a tendency to stabilize lower-spin states is reported (i.e. in
>> the case of the imidazole or chloride ligated molecules triplet and
>> quartet states arise at the b3lyp level, respectively, as opposite to
>> the expected quintet and sextet states. I've performed calculations
>> (partly unpublished, partly published here,that is, actually, not very
>> visible...)
>> Macroheterocycles 2011 4(3) 161-163
>> on different mono and di-iron porphyrin and phthalocyanine complexes.
>> For instance, in the case of the Fe(III) azide and chloride porphyrins
>> I've obtained a sextet spin-state in the case of DFT+U(Fe=4.0 eV, with
>> Quantum ESPRESSO) and B2PLYP/def2-TZVPP (with the ORCA package), and a
>> quartet spin-state in the case of B3LYP/def2-TZVPP (always with ORCA).
>> More examples: there is an interesting family of Co(III) complexes
>> investigated by several authors (including me). You can find several
>> structures in the supporting information of
>> Li and Siegbahn; J. Am. Chem. Soc. 2013, 135, 13804−13813
>> In the case of the tetranuclear Co(III) complex both B3LYP and
>> DFT+U(Co=5.9 eV,O=2.0 eV) indicate a low spin (S=1) result as the most
>> stable configuration. I've published some results, obtained at a
>> restricted open-shell level on the tetranuclear (something in the SI)
>> and (mainly) on larger complexes here
>> Mattioli et al.; J. Am. Chem. Soc. 2013, 135, 15353−15363
>> The interesting thing (and still under investigation) is that in
>> larger Co(III)-oxo clusters the peripheral Co atoms seem not to couple
>> in a low-spin fashion with the other ones, when investigated at DFT+U
>> level, as opposite to the B3LYP case. If you are interested I can send
>> you some more details offline (after tuesday, however). A very similar
>> tetranuclear Ni-oxo compound has been investigated here
>> Cao et al.; PRL 100, 167206 (2008)
>> And a very complex antiferromagnetically-coupled (or broken-symmetry,
>> if you prefer) high-spin has been spotted by DFT+U(Ni,O), and
>> confirmed by comparison of calculated and measured coupling constants J.
>>
>> This said, the world of open shell transition metal complexes is vast,
>> and of course there is something that does not fit in my previous
>> simple solution to Alex's problem. On the other hand, the fact that if
>> you stretch an H2 molecule and use EXX you will obtain overcoupling of
>> electrons is a matter of fact. Anyway, we may discuss again (after
>> next tuesday...) the properties of further compounds.
>>
>> All the best
>>
>> Giuseppe
>>
>> Giuseppe Mattioli
>> ISM-CNR
>> Giuseppe
>>
>>
>>
>>
>>
>> Quoting Jia Chen <jiachenchem at gmail.com>:
>>
>> > 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
>> >> 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>
>> >>
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>> >
>> >
>> >
>> > --
>> > Jia Chen
>>
>>
>> --
>> ********************************************************
>> - 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>
>>
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>
>
>
> --
> Jia Chen
--
********************************************************
- 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>
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