<div dir="ltr"><div><div><div>Dear Giuseppe Mattioli,<br><br></div>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!<br>
<br></div>Bests<br></div>Jia <br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Jan 3, 2014 at 2:13 PM, Giuseppe Mattioli <span dir="ltr"><<a href="mailto:giuseppe.mattioli@ism.cnr.it" target="_blank">giuseppe.mattioli@ism.cnr.it</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
Dear Alex<br>
Paolo is right, of course. Check the convergence on the Re PP first.<br>
I would add a few words anyway. Hybrid DFT/HF functionals like B3LYP<br>
are pretty useful, but in the case of open-shell systems there are<br>
some known limitations. See the very interesting paper by Cohen<br>
(Science Vol. 321 no. 5890 pp. 792-794). The HF exchange term added to<br>
the DFT xc kernel leads to an overcoupling of electron pairs and,<br>
therefore, to an overestimate of the stability of low-spin solutions.<br>
Chemists usually call it a "static correlation" error. As we could<br>
spend years in discussing such an issue, I feel to suggest two simple<br>
tests: try to perform a B2PLYP calculation (if you can afford it) with<br>
your GTO package. The MP2 treatment of B3LYP correlation is supposed<br>
to correct part of the static correlation error. Otherwise, try to<br>
perform a DFT+U calculation with the U correction applied (possibly in<br>
a self-consistent fashion, see the many related papers by Cococcioni,<br>
De Gironcoli, Kulik, Marzari, and mine) to the Re 5d shell (I did<br>
never use Re... Are the 4f electrons embedded in the pseudo?). The<br>
on-site DFT+U method is supposed to be free from sce, or, better, less<br>
affected than its parent DFT functional. If you obtain a high-spin<br>
solution with one of these methods, there are sound reasons, in my<br>
opinion, to trust that it is a stable solution...<br>
HTH<br>
Giuseppe<br>
<br>
Giuseppe Mattioli<br>
ISM-CNR<br>
Italy<br>
<div class="im"><br>
Quoting Alex Granov <<a href="mailto:alex.granov@outlook.com">alex.granov@outlook.com</a>>:<br>
<br>
> Hi<br>
> We are studying an organo-metallic compound which contains 3 Benzene<br>
</div>> rings, phosphorous, oxygen, Iodine, and rhenium atoms.Our quantum<br>
<div><div class="h5">> chemistry study using B3LYP/6-31+G* (Gaussian basis set) shows that<br>
> the ground state of the system is singlet (spin -unpolarized). We<br>
> attempted to optimize this structure using quantum espresso to<br>
> calculate some other electronic properties. Then surprisingly we<br>
> found that the spin-polarized system is more stable than the<br>
> spin-unpolarized one in contrast with our quantum chemistry study.<br>
> In the following you can see my input file and I wonder whether<br>
> there is something wrong in the input that made the very noticeable<br>
> contrast. I appreciate your comments to understand the issue and<br>
> solve it in advance.<br>
> q/e input:&control calculation='relax',<br>
> restart_mode='from_scratch', prefix='Re-Be', pseudo_dir =<br>
> './pseudo/', outdir='./tmp/', tprnfor=.t. ,<br>
> etot_conv_thr=1.0D-4, forc_conv_thr=1.0D-3, nstep=300,<br>
> dt=10, / &system ibrav= 8, a=20, b=20, c=20, nat=37, ntyp=6,<br>
> ecutwfc = 30, ecutrho = 300, occupations='smearing',<br>
> smearing='marzari-vanderbilt', degauss=0.005, nspin=2 ,<br>
> starting_magnetization(1)=1 ,starting_magnetization(2)=1 ,<br>
> starting_magnetization(3)=1 , starting_magnetization(4)=1 ,<br>
> starting_magnetization(5)=1 , starting_magnetization(6)=1 , /<br>
> &electrons conv_thr = 1.0d-6, mixing_beta=0.2,<br>
> mixing_mode=local-TF, / &IONS ion_dynamics="bfgs", upscale=100.0D0<br>
> ,/ATOMIC_SPECIESRe 186.207 Re.pbe-hgh.UPFO 15.999<br>
> O.pbe-rrkjus.UPFC 12.000 C.pbe-rrkjus.UPFH 1.000<br>
> H.pbe-rrkjus.UPFI 126.90 I.pbe-n-rrkjus_psl.0.2.UPFP 30.9737<br>
> P.pbe-n-van.UPFK_POINTS {gamma}<br>
><br>
> -------------------------------------------------Alex<br>
> GranovМосковский физико-технический институт (MIPT)Moscow, Russia<br>
<br>
<br>
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<span class="HOEnZb"><font color="#888888"><br>
Giuseppe Mattioli<br>
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA<br>
v. Salaria Km 29,300 - C.P. 10<br>
I 00015 - Monterotondo Stazione (RM)<br>
Tel <a href="tel:%2B%2039%2006%2090672836" value="+390690672836">+ 39 06 90672836</a> - Fax <a href="tel:%2B39%2006%2090672316" value="+390690672316">+39 06 90672316</a><br>
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