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calculation time for a small system Date: 2020/03/06 18:00 Name: Yongsheng Zhang Dear devlopers, The basis sets of Openmx are LCAO. Generally, it seems that it should be more efficient (or faster) than running the plane-wave based code like VASP. However, it is not the case in small systems. I did a test using a bulk TiO2 structure. It turns out that the vASP code is 2-3 times faster than the OpenMX code. They are using the same k-mesh. I am pretty confused about the reasons behind the significant time difference. Would you please explain it to me? Thanks. CPU-number 2 8 vasp 0.92 0.43 openmx 2.27 0.93 unit: second/scf DATA.PATH /home/yshzhang/software/openmx3.8/DFT_DATA13 System.CurrrentDirectory ./ System.Name tio2 level.of.stdout 1 level.of.fileout 1 scf.restart off Species.Number 2 <Definition.of.Atomic.Species Ti Ti7.0-s2p2 Ti_PBE13 O O5.0-s2p2 O_PBE13 Definition.of.Atomic.Species> Atoms.Number 6 Atoms.SpeciesAndCoordinates.Unit Ang <Atoms.SpeciesAndCoordinates 1 Ti 0.00000000 0.00000000 0.00000000 6.00 6.00 2 Ti 2.31484428 2.31484428 1.47137134 6.00 6.00 3 O 1.40975946 1.40975946 0.00000000 3.00 3.00 4 O 3.21992911 3.21992911 0.00000000 3.00 3.00 5 O 0.90508483 3.72460374 1.47137134 3.00 3.00 6 O 3.72460374 0.90508483 1.47137134 3.00 3.00 Atoms.SpeciesAndCoordinates> Atoms.UnitVectors.Unit Ang <Atoms.UnitVectors 4.62968857 0.00000000 0.00000000 0.00000000 4.62968857 0.00000000 0.00000000 0.00000000 2.94274268 Atoms.UnitVectors> scf.XcType GGA-PBE # LDA|LSDA-CA|LSDA-PW scf.SpinPolarization off # On|Off scf.ElectronicTemperature 300.0 # default=300 (K) scf.energycutoff 300.0 # default=150 (Ry) scf.maxIter 170 # default=40 scf.EigenvalueSolver band # Recursion|Cluster|Band scf.Kgrid 1 1 1 # means 4x4x4 scf.Mixing.Type rmm-diisk # Simple|Rmm-Diis|Gr-Pulay scf.Init.Mixing.Weight 0.010 # default=0.30 scf.Min.Mixing.Weight 0.001 # default=0.001 scf.Max.Mixing.Weight 0.200 # default=0.40 scf.Mixing.History 6 # default=5 scf.Mixing.StartPulay 12 # default=6 scf.criterion 1.0e-9 # default=1.0e-6 (Hartree) scf.system.charge 0.0 # default=0.0

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Re: calculation time for a small system ( No.1 ) Date: 2020/03/08 08:24 Name: T. Ozaki Hi, In general, OpenMX seems to be slower than VASP for small systems with dense crystal structures, since OpenMX does not take account of computational reduction by symmertry. I wonder that OpenMX might be faster than PW codes for systems with low-dimensional structures and sparse crystal structures. Regards, TO Re: calculation time for a small system ( No.2 ) Date: 2020/03/08 22:47 Name: Yongsheng Zhang Thanks. That makes sense. I agree that OpenMX should be faster for the large low-symmetry system. I am wondering why OpenMX does not include symmetries. This would widen the applications of the code? Re: calculation time for a small system ( No.3 ) Date: 2020/03/08 23:13 Name: Yongsheng Zhang Dear Prof. Ozaki, I just realize that I even did the tests using one Gamma-k-point in OpenMX and VASP. In this case, the symmetry operation should have little effects on the computational time. Unfortunately, OpenMX is still slower than VASP. Is that due to the time in building or solving the symmetry dependent interatomic potentials in the two codes? Thanks Yongsheng Re: calculation time for a small system ( No.4 ) Date: 2020/03/09 09:56 Name: T. Ozaki Hi, The elapsed time of each calculation is output in the standard output and the out file. So, you can figure out which part of calculation can be a time-consuming part. Regards, TO

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