Dear Dr. Deyu Lu I am looking for a Ti norm-conserving PSP. I was wondering if I could have the generated Ti-PSP by you.
Best Regards, Mohaddeseh --------------------------------------------------------- Mohaddeseh Abbasnejad, Room No. 323, Department of Physics, University of Tehran, North Karegar Ave., Tehran, P.O. Box: 14395-547- IRAN Tel. No.: +98 21 6111 8634 & Fax No.: +98 21 8800 4781 Cellphone: +98 917 731 7514 E-Mail: m.abbasnejad at gmail.com Website: http://physics.ut.ac.ir --------------------------------------------------------- On Tue, Jun 28, 2011 at 5:57 AM, Deyu Lu <deyulu at yahoo.com> wrote: > Dear PW developers and users: > I have been doing norm-conserving PSP (PBE) calculations to > study the structure of rutile tio2. During my study, I found the > resulting lattice constant is sensitive to some fine details of > the PSPs I used. Such effect is kind of counter-intuitive. Perhaps > someone with a better understanding can clarify it for me. The story is a > bit long, which I summarize below. Input files and some PSPs are attached. > > All the calculations are carried out on a Linux cluster with QE 4.2.1. > The code is compiled with Intel compiler (ifort) and mvapich2-1.2, > and is linked to the mkl library accompanied with the code. Main > results are verified on a Cray XE6 machine (hopper at NERSC) with the same > version of QE. > > The Ti PBE PSP was generated from an ionic configuration > 3s2 3p6 3d0 4s0, with semi-core included explicitly. A small rcut > (0.9 0.9 1.0 for 3s 3p 3d) was used to ensure a good transferability. > The psp was generated from opium, and the convergence can be > reached at ecutwfn=160 Ry. > > The structure of Rutile TiO2 was calculated using this Ti PSP > and O.pbe-mt.UPF from QE library. The lattice constant 4.587 angstrom > is in excellent agreement with experiment (4.587 and 4.582 angstrom) > but at odds with all the known theoretical results (ultrasoft and paw) in > the literature (4.63 - 4.65). The error is about 1.1%. So our good agreement > seems to be accidental. In order to obtain a better understanding, I > performed the calculations using paw (vasp) and norm-conserving PSP with HGH > (abinit library Theor. Chem. Acc. 114, 145 (2005)) which is known to be very > accurate. Indeed, the results are consistent with literature. > > The 1% difference was later found to be related to the Oxygen PSP. > Different Oxygen PSPs are used in the following tests. > > 1.d: 08-O.PBE.fhi.UPF (abinit PSP library, converted to UPF, lmax=3, > local=2) > a=4.633 angstrom > > 2.d: O.pbe-mt.UPF (QE PSP library, lmax=2, local=2) > a=4.587 angstrom > > In order to see if the f channel can cause any difference, 08-O.PBE.fhi.UPF > is modified (08-O.PBE.fake.UPF) by removing f channel and making > corresponding changes in DIJ. > No difference is found as compared to 1.d. > > 6.d: 08-O.PBE.fake.UPF (modified version, lmax=2, local=2) > a=4.633 angstrom > > There seems to be a bug in the <PP_HEADER> section of O.pbe-mt.UPF, where > Max angular momentum component is set to 1 instead of 2. I manually changed > it to 2 (O.pbe-mt.9.UPF), and no difference found in output as compared to > 2.d. So this field is not sensitive in the calculation. > > 9.d: O.pbe-mt.9.UPF (minor modification of O.pbe-mt.UPF) > a=4.587 angstrom > > In the rest of tests, the "Max angular momentum component" is left > unchanged. > > To find out the difference between 08-O.PBE.fake.UPF and O.pbe-mt.UPF, I > plot term by term for two PSPs, and the results are shown in the xmgrace > plots for mesh, local, and nonlocal parts of the PSP. The two meshes have > the same size, with a max difference within 5d-3 a.u (mesh.agr). There is no > difference found in local and non-local components of the PSP (local.agr and > nonlocal.agr). In the inset of local.agr, we see that even the small wiggle > at the origin is id > entical. My conclusion is that the two PSPs are literally the same. > > Further tests were done by replace local PP and Beta sections in > O.pbe-mt.UPF one by one by the corresponding section from 08-O.PBE.fake.UPF, > and the difference is negligible as compared to 2.d. > > In the end, I replaced </PP_MESH> section in O.pbe-mt.UPF with that from > 08-O.PBE.fake.UPF, and kept everything else unchanged, the lattice constant > increased from 4.587 to 4.633. > > 8.d: O.pbe-mt.8.UPF ( </PP_MESH> section modified) > a=4.633 > > In the end, I was quite confused about the fact that a very small change in > the mesh (<5d-3 max at 80 a.u.) can cause a difference in the lattice > constant by 1%. > > Best > Deyu Lu > > ************************************************ > Deyu Lu > Assistant Physicist, Theory & Computation Group > the Center for Functional Nanomaterials > Building 735, Brookhaven National Lab > Upton, NY, 11973 > ************************************************ > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > -------------- next part -------------- An HTML attachment was scrubbed... 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