Re: [SIESTA-L] DZP basis for elements with semicore states
On Wed, 23 Jan 2008, X. Feng wrote: | Hi Andrei, | | Thanks a lot for the explainations and the example for Cr. | | SIESTA manuel mentioned that to generate a polarization | orbital one needs to use P in PAO.Basis. Right | However, I saw | from Siesta website that in some of the optimized basis sets, | for example Ti and Mn, only a normal single zeta (4p) is used | as a polarization orbital. Then it is probably not a polarization orbital in a strict sence, derived from an s-orbital distorted by electric field. Rather, this is an orbital of p-angular symmetry, with radial dependence obtained or tuned I do not know how. | It is mentioned in the notes for these | bases that this normal single zeta is intended for polarization. What fo you mean by intended for polarization? Who intends to polarize whom? Can you give a reference? | Of course, this is not the definition of | a polarization orbital in the SIESTA manuel. No, it isn't. But from the point of view of Siesta, there are no fixed rules as for how to construct basis. You can draw you basis function by hand (, difitalize it) and go ahead with calculations. The question is, how good this basis would be. The standard scheme (DZP, Energy shift) is merely a reasonably good and fool-proof algorithm. | I don't know the reason | why people use a normal single zeta rather than following the manuel. Because they either believe that their tuned basis is more efficient, or they specifically want to use minimal basis, and they need to tune its functions as good as they can. | Is it better in some cases? Or, it is not a justified method? Depends on your definition of better and on cases in question. What do you want to achieve and at which price? The optimization of basis sets in any method using atom-type orbitals is a bit problematic. | By the way, do you have a tested basis sets for Cr, V? I did not tune them myself, if that's what you mean. However, I test basis sets (either standard, or borrowed from people) with respect to the tasks I have in mind for these elements. | I have pseudopotential for Cr and V without semicore states. | The magnetic moments are too high, so semicore states are necessary. This is a wrong argumentation. 3p semicore in Cr, V is not likely to affect your magnetic moment in a noticeable way, because 3p remains fully occupied. You'll see this if you compare total magnetic moments. So if your magnetic moments are too high it must be due to a different rason. Of course you may see that the figures for local magnetic moments, according to Mulliken populations, vary a bit as you vary basis functions, but this is due to ambigous definition of local magnetic moment, and has nothing to do with semicore as such. On the contrary, the presence of semicore may be quite important for comparing energies of different phases (e.g., magnetic phases), for getting right relaxation lattice constant (say, you may be 2-5% off the exp. volume with semicore and 15% off without it). | I'm currently testing PP's for Cr and V from a publication with | DZP, which will be generated by the method I learned today. | I'll be very grateful if you can send me PP's and basis, if you | have some. There is a PP + basis repository at the Siesta web site, and a lot of previous enquiries in the mailing list. Moreover, usually in their publications people describe what basis and PP they used. So if you want to profit from somebody's particular tuning for a particular system, you can write to people directly. You see, even for your Cr and V, the basis (and particularily whether you need semicore or not) depends so much on what you need (band sructure? phase diagram? phonons? transport?) and in which systems (bulk metals? clusters? organometallic molecules?) Good luck Andrei +-- Dr. Andrei Postnikov Tel. +33-387315873 - mobile +33-666784053 ---+ | Paul Verlaine University - Institute de Physique Electronique et Chimie, | | Laboratoire de Physique des Milieux Denses, 1 Bd Arago, F-57078 Metz, France | +-- [EMAIL PROTECTED] -- http://www.home.uni-osnabrueck.de/apostnik/ --+
Re: [SIESTA-L] pseudopotential for Pt
Dear Mohammad, there was a question about pseudopotential for platinum before. I think Javier Junquera gave an input for the ATOM program to create LDA pseudopotential for platinum and also a basis set for platinum. So here it is: INPUT FOR ATOM: pe Platinum tm2 n=Pt c=car 0.0 0.0 0.0 0.0 0.0 0.0 124 60 1.00 0.00 61 0.00 0.00 52 9.00 0.00 53 0.00 0.00 2.35 2.50 1.24 2.35 0.0 1.7 and basis set: %block PAO.Basis Pt 3 0.06506 n=6 0 2 E35.28484 6.29031 6.85818 5.34263 1.0 1.0 n=6 1 1 E10.02220 2.26448 7.56445 1.0 n=5 2 2 E30.91888 6.56288 7.13150 5.56464 1.0 1.0 %EndBlock PAO.Basis When you use ATOM, be careful about the format of the input file, it is quite rigid. Good luck Bozidar
Re: [SIESTA-L] DZP basis for elements with semicore states
Hi Marcos, Thank you very much for the reply. I know that a polarization orbital generated by siesta is obtained by solving Schroedinger equation with an electric field. However, people are using a normal single zeta, for example the basis sets for Mn and Ti on the siesta website, for the purpose of a polarization orbital. I really don't know the reason. Why not using P in Pao.Basis? In your example in the last email you also used normal zeta for polarization. The following is part of the Ti basis from siesta website. %block PAO.Basis Ti5 1.91 ... n=402 E 96.47 5.60 6.099963989753075.09944363262274 n=411 E 0.50 1.77 3.05365979938936 %endblock PAO.Basis How about do it this way, the way explained in the manuel: %block PAO.Basis Ti5 1.91 ... n=4 0 2 P 1 E 96.47 5.60 6.099963989753075.09944363262274 %endblock PAO.Basis Another question is : usually a default DZP for a PP without semicore states is good enough. For PP with semicore states we can also let siesta generate a DZP basis. I don't know if the quality is also good enough in this case. Thanks again, Regards, Xiaobing Quoting Marcos Verissimo Alves [EMAIL PROTECTED]: Feng, Sorry if I'll be too basic but I have to confess I don't get exactly what you tried to say about the polarization orbitals. The thing is, polarization orbitals (PO) are the solution to the perturbative problem of the atom in a weak electric field. So, to find the PO the perturbation problem is solved numerically and its solution is the l+1 orbital. The rc for this orbital is probably determined directly from the numerical solution that siesta obtains. Now, the other way of doing it is by considering the analytical solution and determining the rc yourself. Either way, when you start your calculation, no electric field is used, unless you specifically tell siesta to do so. That is, the PO, once determined, are orbitals just like any other, the KS solving process doesn't even know that once upon a time there was an electric field to generate the PO :D Of course, I would say that optimising the PO's rc's would definitely give better results, at least in principle. In principle because you could have a huge lucky star and get a very good basis set by just using an appropriate value for the EnergyShift... :) However, I guess this could be very unlikely. However, bear in mind that this is just my opinion, and the ppl who are more knowledgeable on basis set issues could well give a counter-argument. Cheers, Marcos Vous avez écrit / You have written / Lei ha scritto / Você escreveu... X. Feng Hi Marcos, Thanks very much for the reply, it is really very helpful to me. I noticed that a lot people are not using P in Pao.Basis to generate polarization orbital, rather they use, like in your example, a normal single zeta orbital. With P the radius cannot be freely changed, but it is polarized by using an electric field. So, this means that the radius of a polarization orbital is more important than polarization by electric field. Is it right? In terms of accuracy, do you think the method for polarization in your example is better than P method? (assuming that the basis sets for both methods are optimized) Thanks again, Yours Xiaobing Quoting Marcos Verissimo Alves [EMAIL PROTECTED]: Hi Xiaobing, In principle, this should be it. Unless you have sometthing in mind for a particular orbital or even a zeta, in which case you can set it with a certain rc and let the others be determined by siesta. This is useful, for example, if you want to explicitly control the extension of your polarisation orbitals: instead of having n= 3 0 2 P 0.000 0.000 1.000 1.000 you include an orbital with a unit of angular momentum higher than the one it polarizes: n= 3 0 2 0.000 0.000 1.000 1.000 n= 3 1 1# -- Single polarization for the 3s orbital above 0.000 # double polarization would be two zetas 1.000 and set the rc explicitly. I'm not sure now, but I think that sometimes siesta can complain about the rc's of polarization orbitals included in this manner, telling you to set their rc explicitly. Cheers, Marcos Vous avez écrit / You have written / Lei ha scritto / Você escreveu... X. Feng Dear everyone, Some people used DZP basis (not optimized) for some transition metals with semicore states, like V, Cr. I don't know how they do it. Is it simply to set all cutoff radii to zeroes in the PAO.Basis and let SIESTA to generate these radii? One can only use hard confinement this way. Could somebody having such experience give me a clarification? Many thanks in advance. Yours, Xiaobing This
[SIESTA-L] pseudopotential for Pt
Dear Siesta users, Does anyone have a pseudopotential for platinum? Thanks a lot for your help. Mohammad
