Re: [SIESTA-L] About PDOS for 2p orbitals
Perhaps a more physical way to look at things would be to use the maximally localized Wannier functions (which are quite similar but have a more molecular meaning). How exactly to do that? Or you mean exactly looking at LDOS of some energy region?
Re: [SIESTA-L] Why it is so hard to converge with 32 atom unit cell.
On Tue, 5 Dec 2006, Vasilii Artyukhov wrote: | Finally, a word regarding the k-point grids: although a dense k-point grid | is essential for an adequate description of properties of metals, I don't | think that denser grids could help you improve your SCF convergence, since | the SCF equations are solved at each k-point independently (which is why the | k-point parallelization is so efficient). A comment on this: in my understanding, not the SCF equations are solved at each k-point independently, but the Kohn-Sham equations which are only part of the SCF loop (if we discuss the conventional diagonalization scheme). Then, in order to find the Fermi energy and re-define the density matrix, the information is needed over all k-points. If the k-mesh is sparse - and the system is metal - then a too high weight attributed to a given k-point, in which a given band might happen to be either occupied, or empty, would lead to additional fluctuations/instability. More dense k-mesh reduces the importance of every single k-point and thus stabilizes the convergence. Of course by intruducung a large enough artificial smearing (Electronic Temperature) one can suppress this instability, at the expence of overall precision. Probably that's OK in order to enforce some initial convergence. The exact behavior and the balance of these factors is of course up to a system in question. Best regards, Andrei Postnikov +-- 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] About PDOS for 2p orbitals
2006/12/4, Oleksandr Voznyy [EMAIL PROTECTED]: I still haven't got any reasonable explanation from other people. The only suggestion I hear many times that hybridization concept is oversimplified and you need to think of molecular orbitals rather than simple hybridization of atomic orbitals. That's more or less true, since the hybrid orbitals are basically a set of linear combinations of atomic functions satisfying a certain localization criterion in a free atom. Perhaps a more physical way to look at things would be to use the maximally localized Wannier functions (which are quite similar but have a more molecular meaning).
Re: [SIESTA-L] Why it is so hard to converge with 32 atom unit cell.
+-- 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/ --+ On Tue, 5 Dec 2006, siesta88 wrote: | Dear SIESTA users: | I used dzp atomic basis,160 ry meshcutoff ,30 Bohr kgrid cutoff to calculate FePt system(see the pictures of my unit cell in attachment), however, it seems to take forever to converge with the SCF cycle. dDMax(around 1.0) stays far beyond tolerence (0.1), and if I increase the cell to 108 atom unit cell(3x3x3 supercell), dDmax becomes even larger. Yet the simplest unit cell with 4 atoms converges fine. | | Here is a fragment of my SCF cycle: | siesta: 42 -25183.5213 -24873.4575 -24873.4883 1.2337 -2.1597 | siesta: 43 -25153.3555 -24872.5874 -24872.6213 1.0953 -1.7754 | siesta: 44 -25204.6434 -24870.7750 -24870.8201 1.0794 -2.1741 | siesta: 45 -25174.8238 -24868.9171 -24868.9419 1.3392 -2.3371 | siesta: 46 -25138.7377 -24868.4595 -24868.4879 1.0200 -2.1080 | siesta: 47 -25177.5378 -24866.3887 -24866.4199 1.1245 -1.9894 | siesta: 48 -25159.6251 -24865.8291 -24865.8733 1.0482 -2.0247 | siesta: 49 -25206.9572 -24864.1873 -24864.2264 1.0436 -2.1378 Dear SuiYang: Your mixing parameter is too large redata: New DM Mixing Weight = 0.2500 that's why (at least) you get no convergence. Try to set DM.MixingWeight.05 (or less), to begin with. There are two important issues to consider: 1) in a large supercell, there is genererally more difficult to achieve convergence because you have many bands with contributions from similar atoms around the Fermi level. So the system has a tendency to swap charge from one atom to another, which effect you might need to damp more eficiently than was the case in a smaller cell. In the single cell with only few bands and few atoms, you won't normally have this degree of freedom in your system, so the convergency goes sraightforwardly. 2) In a metal system, depending on the actual band sructure, the accuracy of the k-summation/interation becomes an important issue influencing the accuracy of your result, and the convergence to it. In SIESTA where no tetrahedra integration is available, you must carefully test the effect of increasing number of k-points, and the energy broadening used in the search for the Fermi level. Your present choice 5*5*5 k-points with ElectronicTemperature 300 K is not a priori unreasonable for getting a preliminary convergence, but be careful to make additional tests if you want to extract some energy differences afterwards. Best regards, Andrei Postnikov +-- 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] Why it is so hard to converge with 32 atom unit cell.
you can tune parameters : DM.MixingWeight and DM.NumberPulay On 12/5/06, siesta88 [EMAIL PROTECTED] wrote: Dear SIESTA users: I used dzp atomic basis,160 ry meshcutoff ,30 Bohr kgrid cutoff to calculate FePt system(see the pictures of my unit cell in attachment), however, it seems to take forever to converge with the SCF cycle. dDMax(around 1.0) stays far beyond tolerence (0.1), and if I increase the cell to 108 atom unit cell(3x3x3 supercell), dDmax becomes even larger. Yet the simplest unit cell with 4 atoms converges fine. I also used szp atomic basis,spin polarized and larger cutoff(300 ry meshcutoff,40 Bohr kgrid cutoff ) with 32 atom cell, the problem is still the same, it seems to have nothing to do with the cutoff I choose. Could anyone give me a clue where the problem might lie? I would really appericiate your help. If it doesn't converge, the forces and stress are wrong and so is the later MD steps. Here is a fragment of my SCF cycle: siesta: 42 -25183.5213 -24873.4575 -24873.4883 1.2337 -2.1597 siesta: 43 -25153.3555 -24872.5874 -24872.6213 1.0953 -1.7754 siesta: 44 -25204.6434 -24870.7750 -24870.8201 1.0794 -2.1741 siesta: 45 -25174.8238 -24868.9171 -24868.9419 1.3392 -2.3371 siesta: 46 -25138.7377 -24868.4595 -24868.4879 1.0200 -2.1080 siesta: 47 -25177.5378 -24866.3887 -24866.4199 1.1245 -1.9894 siesta: 48 -25159.6251 -24865.8291 -24865.8733 1.0482 -2.0247 siesta: 49 -25206.9572 -24864.1873 -24864.2264 1.0436 -2.1378 I attached the output file and pictures of the unit cell I used. Generally speaking, the atomic position is the same as FCC crystal, only that a=b,c= 0.95a, because of the ordering alignment of Fe and Pt ( a layer of Fe then a layer of Pt along the c-axis) -- SuiYang 2006-12-05 -- Hai-Ping Lan Department of Electronics , Peking University , Bejing, 100871
[SIESTA-L] Why it is so hard to converge with 32 atom unit cell.
Dear SIESTA users: I used dzp atomic basis,160 ry meshcutoff ,30 Bohr kgrid cutoff to calculate FePt system(see the pictures of my unit cell in attachment), however, it seems to take forever to converge with the SCF cycle. dDMax(around 1.0) stays far beyond tolerence (0.1), and if I increase the cell to 108 atom unit cell(3x3x3 supercell), dDmax becomes even larger. Yet the simplest unit cell with 4 atoms converges fine. I also used szp atomic basis,spin polarized and larger cutoff(300 ry meshcutoff,40 Bohr kgrid cutoff ) with 32 atom cell, the problem is still the same, it seems to have nothing to do with the cutoff I choose. Could anyone give me a clue where the problem might lie? I would really appericiate your help. If it doesn't converge, the forces and stress are wrong and so is the later MD steps. Here is a fragment of my SCF cycle: siesta: 42 -25183.5213 -24873.4575 -24873.4883 1.2337 -2.1597 siesta: 43 -25153.3555 -24872.5874 -24872.6213 1.0953 -1.7754 siesta: 44 -25204.6434 -24870.7750 -24870.8201 1.0794 -2.1741 siesta: 45 -25174.8238 -24868.9171 -24868.9419 1.3392 -2.3371 siesta: 46 -25138.7377 -24868.4595 -24868.4879 1.0200 -2.1080 siesta: 47 -25177.5378 -24866.3887 -24866.4199 1.1245 -1.9894 siesta: 48 -25159.6251 -24865.8291 -24865.8733 1.0482 -2.0247 siesta: 49 -25206.9572 -24864.1873 -24864.2264 1.0436 -2.1378 I attached the output file and pictures of the unit cell I used. Generally speaking, the atomic position is the same as FCC crystal, only that a=b,c=0.95a, because of the ordering alignment of Fe and Pt ( a layer of Fe then a layer of Pt along the c-axis) SuiYang 2006-12-05 FePtsuper2.out Description: Binary data attachment: 2.JPGattachment: 1.JPG
Re: [SIESTA-L] HELP-- the pseudopential for Rh
Hi Marcos,
Thanks for your reply. I add the 4s into the valence as semicore--maybe
this is not correct. however the lattice constant is 3.8358 with an error 1%
comparing with the exp value, in fact, i am confused how to decide the valence
electron configuration. Do you mind sending your pesudopential of Rh to me for
comparse? your help is appreciated!
regards
H.F Wang
Marcos Verissimo Alves [EMAIL PROTECTED] 写道：
Hi Wang,
Your input seems a bit strange to me, but I could be wrong, of course. The
electronic config of Rh is
[Ar]{3d10 4s2 4p6} 4d8 5s1 ,
where I have inserted the possible semicore states in braces. Looking at
the webelements site, the energy diagram for the orbitals would be such
that 4p6 would be worth putting into valence as semicore. In your input
file I do not see the 5s1 orbital. Maybe, instead of
4 0 2.00 0.00
you should insert
5 0 1.00 0.00
Does your pseudopotential give good results for bulk Rh (bulk modulus,
lattice parameter, band structure...)? Also, check for BSSE corrections
when calculating chemisorption energies.
Cheers,
Marcos
hello colleagues:
using the pseudopential generated by meself, i did calculation on
oxygen adsorption on Rh(111), but i found the chemisorption energy is
much lower than that reported in the literature. i added the semicore
into the pseudopential, the Rh-semi.inp is as follows:
pg Rhodium
tm2 0.00
n=Rh c=car
0.0 0.0 0.0 0.0 0.0 0.0
7 5
4 0 2.00 0.00
4 1 6.00 0.00
4 2 8.00 0.00
4 3 0.00 0.00
2.08 2.08 2.30 2.57 0.0 0.0
now i want to know how to correct the drawback, could everyone provide
me your input parameter for the pseudopential of Rh to make a benchmark?
The one without semicore added is also appreciated.
Thanks in advance!
H.F. Wang
-
Mp3疯狂搜-新歌热歌高速下
--
Dr. Marcos Verissimo Alves
Post-Doctoral Fellow
Condensed Matter and Statistical Physics Sector
International Centre for Theoretical Physics
Trieste, Italy
I have become so addicted to vi that I try to exit OpenOffice by typing :wq!
-
Mp3疯狂搜-新歌热歌高速下
