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Elastic Constant of Cu - 6.0Hs3p3d3 Date: 2019/06/17 16:58 Name: C. Pashartis Hello, I have been using openmx to calculate elastic constants of various elements. So far I have had success in this regard but occasionally I'll stumble upon a situation where I have to fine tune some input parameters in comparison to those given on your VPS/PAO convergence tests. One such case I can't seem to resolve is the curious case of Cu-6.0H-s3p3d3. It seems I have stumbled on a region of numerical noise that fluctuates with 30 GPa. I have tried to change smearing temperature, scf tolerances, cutoff energy, k-points, and force tolerances. My assumption at this point is that perhaps I am using over-converged basis sets. It seems people in the past had trouble with Cu basis sets, not sure if they are resolved. Is there anything else you would think of that may help. I am using openmx-3.8 P.S. I appreciate your help! Below is a sample input file: FOR RELAXATION: # # SCF # scf.Kgrid 36 36 36 scf.XcType GGA-PBE scf.SpinPolarization off scf.energycutoff 700 scf.ElectronicTemperature 300 scf.maxIter 100 scf.EigenvalueSolver band scf.Mixing.Type Rmm-Diisk scf.criterion 1e-06 scf.restart off scf.partialCoreCorrection on scf.Mixing.History 20 scf.Mixing.StartPulay 6 scf.Init.Mixing.Weight 0.3 scf.Min.Mixing.Weight 0.001 scf.Max.Mixing.Weight 0.4 scf.lapack.dste dstevx scf.Mixing.EveryPulay 1 scf.fixed.grid 0.0 0.0 0.0 scf.stress.tensor on # # MD # MD.Type RFC5 MD.maxIter 100 MD.Opt.DIIS.History 3 MD.Opt.StartDIIS 5 MD.TimeStep 0.5 MD.Opt.criterion 0.0001 FOR INTERNAL RELAXATION OF DEFORMATION (USUALLY DOESN'T CHANGE ANYTHING) # # MD # MD.Type DIIS MD.maxIter 100 MD.Opt.DIIS.History 3 MD.Opt.StartDIIS 5 MD.TimeStep 0.5 MD.Opt.criterion 0.0001

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Re: Elastic Constant of Cu - 6.0Hs3p3d3 ( No.1 ) Date: 2019/06/20 23:51 Name: T. Ozaki Hi, In a dense structure such as FCC, HCP, and BCC with a small lattice constant, eigenvalues of overlap matrix approach to zero, and sometime they become even negative values. The situation is called overcompleteness of basis functions, and a numerical instability may appear. Then, changing parameters such as temperature, k-points, and scf criteria does not resolve the overcompleteness. Reducing the basis functions can solve the problem. I wonder that s3p3d2 works well for your purpose. Best regards, TO Re: Elastic Constant of Cu - 6.0Hs3p3d3 ( No.2 ) Date: 2019/06/21 20:14 Name: C. Pashartis Hello Prof. Ozaki, Thank you for your response. For the most part, I have been following the basis set schemes that your project has shown on the website in comparison to WIEN2K for the equation of state (varying lattice and plotting energy). I believe this to be a good starting spot for my calculations given that I deform my structure in a non-isotropic fashion. I believe the over-completeness to still be occurring for s2p2d2, am I correct in assuming that the s3p3d2 should then not work either? What are my other options given that it seems the s2p2d2 scheme won't work either? I did also try s3p3d3 on the soft version, however, the results aren't as accurate in elastic properties compared to literature. Which can be inferred from the difference in the equation of state to WIEN2K.

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