Dear Zhen, yes you are right. You have already run your calculations, and get a large spin polarization.
Now run another one, with the two flags indicated. If turning on those flags gives you lower energy, then the spin-polarized result is a metastable ground state, as Marcos indicated. In that case, always keep these flags and move on. Best regards, -Salvador. ----- Original Message ----- From: "Zhen Huang" <[email protected]> To: [email protected] Sent: Wednesday, March 3, 2010 10:39:58 AM GMT -05:00 US/Canada Eastern Subject: Re: [SIESTA-L] Fwd: Titanium Phonon Calculation Re: Titanium calculation help posted earlier Dear Both- A little bit confused. So Salvador you are saying I can run two tests. one w/o totalspin and fix spin one w/. If the one w/ totalspin 0.0 and fixspin true give lower total energy, I can move on to phonon calculation? Thanks Best Regards ------- Zhen (Alex) Huang Ph.D. Student Nanoscale Transport Research Group Laboratory for Computational Methods in Emerging Technologies Cooling Technologies Research Center School of Mechanical Engineering Purdue University Tel: 765 237 9733 On Wed, Mar 3, 2010 at 10:17 AM, Barraza-lopez, Salvador < [email protected] > wrote: Dear Zheng and Marcos, To check Marcos' point one could add the following lines to the input file: totalspin 0.0 fixspin True If the total energy with with these added lines is bigger (in absolute value) than the one you have just obtained, then you are fine, and just need to use this constraint all the time. Best regards, -Salvador. ----- Original Message ----- From: "Marcos Veríssimo Alves" < [email protected] > To: [email protected] Sent: Wednesday, March 3, 2010 9:43:32 AM GMT -05:00 US/Canada Eastern Subject: Re: [SIESTA-L] Fwd: Titanium Phonon Calculation Re: Titanium calculation help posted earlier Salvador and Zhen, Forgive me if I'm wrong, but couldn't magnetic states be displayed in DFT calculations even if the material is not magnetic in its ground states? This could simply be a metastable ground state, and in this case what one should really compare is the total energy of the system in both states, magnetic and paramagnetic. What would really worry me is if, metallic Ti being paramagnetic, the magnetic state were lower in energy. And, on a personal note, I'd trust more the Abinit pseudo than the one generated in a plug-and-play fashion by the Octopus website - there is always a tendency to use the rc's supplied by default in the interface, which are not necessarily good ones. Moreover, the Octopus website interface to the pseudopotential generator allows for less flexibility than a mastery of the ATOM program file format. Abinit pseudos are often tried and tested, even though it is imperative to test every pseudo in simple cases before going for the real thing. Just my 10 cents on the subject. Cheers, Marcos On Wed, Mar 3, 2010 at 3:21 PM, Barraza-lopez, Salvador < [email protected] > wrote: > > Dear Zhen, > I would recommend that you change the cuttof radii in your pseudo and > regenerate it (perhaps 2.0 radii for all your channels, but you can play > with it). Then test it again for polarization in the bulk. > If you never get spin polarization to be zero, try turning on relativistic > corrections, and even core corrections. Just be methodic and go for each of > these things (radii, relativistic corrections, core corrections) > sequentially. The atom manual should be sufficient to guide you in the > process. The process should be: Generate your pseudo with atom, run a SIESTA > calculation with that one and record the magnetization with a standard basis > set, if polarization is not zero, go back and generate a new pseudo, and > iterate as needed. > > Whenever your polarization is zero, you'll discover that the lattice > constant in the bulk should be reasonable; then you can proceed to study > phonon dispersions. > > Best regards, > -Salvador. > > > > ----- Original Message ----- > From: "Zhen Huang" < [email protected] > > To: [email protected] > Sent: Tuesday, March 2, 2010 8:20:42 PM GMT -05:00 US/Canada Eastern > Subject: Re: [SIESTA-L] Fwd: Titanium Phonon Calculation Re: Titanium > calculation help posted earlier > > Dear Salvador- > I turned on the spin-polarized. I find the Qup-Qdown is not zero. > siesta: Total spin polarization (Qup-Qdown) = 4.856526. I am using GGA > PBE generated from http://www.tddft.org/programs/octopus/pseudo.php Lodger > radii 3. I also tried the GGA psf converted from ABINIT which I download > from SIESTA website the Qup-Qdown is about 4.939. Can you let me know how > can I fix this? Thanks. > Best Regards > ------- > Zhen (Alex) Huang > Ph.D. Student > Nanoscale Transport Research Group > Laboratory for Computational Methods in Emerging Technologies > Cooling Technologies Research Center > School of Mechanical Engineering > Purdue University > Tel: 765 237 9733 > > > On Mon, Mar 1, 2010 at 10:14 AM, Barraza-lopez, Salvador > < [email protected] > wrote: >> >> Hi all, >> >> >> >> I've been following this post and want to mention something else that has >> not come out yet. Ti has in the valence two d and two s electrons. >> d-electrons are responsible for magnetic behavior. So, I'd like to ask: Have >> you taken your Ti pseudo (is it LDA, GGA pseudo?) and ran a >> spin-polarized(!) bulk calculation on the HCP phase (two atoms in unit cell) >> ? Don't worry about the basis now, just use the standard one. >> >> >> >> If you've done this, is your total spin up minus spin down is equal to >> zero? >> >> Titanium should be non-magnetic. If you get a large spin polarization >> here, there is no point in keep going further. >> >> If you are sure your bulk Ti run is non-magnetic, please disregard my >> post. >> >> >> >> Best regards, >> >> -Salvador. >> >> ----- Original Message ----- >> From: "Zhen Huang" < [email protected] > >> To: "SiestaMailingList" < [email protected] > >> Sent: Monday, March 1, 2010 8:19:00 AM GMT -05:00 US/Canada Eastern >> Subject: [SIESTA-L] Fwd: Titanium Phonon Calculation Re: Titanium >> calculation help posted earlier >> >> Dear Friends- >> I had trouble of reply my old post. This is a following question about >> Titanium. After I increased the kgrid_cutoff to 25 Ang. The results do >> become better. However, when I am running 3*3*3 supercell calculation the >> dispersion curve becomes like attached. I am running a 5×5*5 case (on 4 >> processors) now however, the calculation becomes really slow. I wonder what >> is the best way to run it faster. Again my input files are attached. Please >> give me some advice. Further, shall I comment kgrid_cutoff in vibrational >> properties calculation? I tried it but it gives me totally wrong results. I >> wonder if I can speed up the calculation by doing anything. I deeply >> appreciate your help. >> >> Best Regards >> ------- >> Zhen (Alex) Huang >> Ph.D. Student >> Nanoscale Transport Research Group >> Laboratory for Computational Methods in Emerging Technologies >> Cooling Technologies Research Center >> School of Mechanical Engineering >> Purdue University >> Tel: 765 237 9733 >> >> >> >> -- >> Salvador Barraza-Lopez >> Postdoctoral Fellow >> School of Physics >> The Georgia Institute of Technology >> >> Office N205 >> 837 State Street Atlanta, Georgia 30332-0430 U.S.A >> Tel: (404) 894-0892 Fax: (404) 894-9958
