Iterative solution of KS equations (with a given threshold) limits the number of significant figures in both energy and properties values. The total energy is less sensitive than property values are. What happens is the following: you *gradients* have limited accuracy -- beyond threshold the digits are largely random. These errors propagate and accumulate throughout geometry optimization.
-- Ilya On Wed, Dec 28, 2016 at 7:45 AM, Pablo García Risueño <[email protected]> wrote: > Dear Espresso community > > I have one problem that is important for me; it is somewhat surprising. I > run geometry optimization (relax) calculations with pw.x with identical > input files, and I obtain rather different final coordinates. The problem > does not happen if ecutwfc is 30, but it does appear for cutoffs of 60, 80 > or 90. Below one can see the exact input file, and examples of the > difference between the final coordinates for both runs (both run with > identical input) for given cutoffs. > > Could anybody give me a clue on the origin of the problem, and how to solve > it? > > Thank you very much. Best regards. > > > > Input file: > > > > &CONTROL > > calculation = 'relax', > > restart_mode = 'from_scratch', > > prefix='', > > outdir = './', > > pseudo_dir = '/path_xxx/PP/', > > forc_conv_thr = 1.0D-6 , > > etot_conv_thr = 1.0D-8 , > > / > > &system > > ibrav = 0, a=18.0, > > nat= 26, ntyp= 2, > > ecutwfc = 30d0, > > nbnd = 100, > > / > > &electrons > > conv_thr = 1.0e-9, > > mixing_beta = 0.7, > > mixing_mode = 'plain', > > diagonalization = 'cg' > > / > > &IONS > > / > > > > ATOMIC_SPECIES > > C 12.0107 C.pz-vbc.UPF > > H 1.007825035 H.pz-vbc.UPF > > > > ATOMIC_POSITIONS { angstrom } > > C 8.891700e+00 8.891700e+00 8.891700e+00 > > C 9.783400e+00 9.783400e+00 8.000000e+00 > > C 9.783400e+00 8.000000e+00 9.783400e+00 > > C 8.000000e+00 9.783400e+00 9.783400e+00 > > C 8.891700e+00 1.067510e+01 1.067510e+01 > > C 1.067510e+01 1.067510e+01 8.891700e+00 > > C 1.067510e+01 8.891700e+00 1.067510e+01 > > C 9.783400e+00 1.156680e+01 9.783400e+00 > > C 9.783400e+00 9.783400e+00 1.156680e+01 > > C 1.156680e+01 9.783400e+00 9.783400e+00 > > H 8.391700e+00 8.391700e+00 8.391700e+00 > > H 7.500000e+00 1.028340e+01 9.283400e+00 > > H 7.500000e+00 9.283400e+00 1.028340e+01 > > H 9.283400e+00 1.028340e+01 7.500000e+00 > > H 1.028340e+01 9.283400e+00 7.500000e+00 > > H 9.283400e+00 7.500000e+00 1.028340e+01 > > H 1.028340e+01 7.500000e+00 9.283400e+00 > > H 9.283400e+00 1.206680e+01 9.283400e+00 > > H 1.206680e+01 9.283400e+00 9.283400e+00 > > H 9.283400e+00 9.283400e+00 1.206680e+01 > > H 8.391700e+00 1.117510e+01 1.117510e+01 > > H 1.117510e+01 1.117510e+01 8.391700e+00 > > H 1.117510e+01 8.391700e+00 1.117510e+01 > > H 1.028340e+01 1.206680e+01 1.028340e+01 > > H 1.028340e+01 1.028340e+01 1.206680e+01 > > H 1.206680e+01 1.028340e+01 1.028340e+01 > > > > > > CELL_PARAMETERS {cubic} > > 1.00 0.00 0.00 > > 0.00 1.00 0.00 > > 0.00 0.00 1.00 > > > > K_POINTS {gamma} {automatic} > > 1 1 1 0 0 0 > > > > > > The program is run with > > > > mpirun -np 32 /path_xxx/pw.x > > > > Final coordinates: The first two rows for ecutwfc=30 for two runs with > identical input are: > > ATOMIC_POSITIONS (angstrom) > C 8.898432121 8.898432121 8.898432121 > C 9.783306562 9.783306562 8.019670107 > > ATOMIC_POSITIONS (angstrom) > C 8.898432121 8.898432121 8.898432121 > C 9.783306562 9.783306562 8.019670109 > > > Final coordinates: The first two rows for ecutwfc=60 for two runs with > identical input are: > > ATOMIC_POSITIONS (angstrom) > C 8.904988579 8.904988579 8.904988579 > C 9.783426086 9.783426086 8.031809869 > > ATOMIC_POSITIONS (angstrom) > C 8.904962246 8.904962246 8.904962246 > C 9.783425401 9.783425401 8.031847251 > > -- > -- > > Dr. Pablo García Risueño > > Institut für Physikalische Chemie, Universität Hamburg, Grindelallee 117, > 20146 Hamburg > > Tel. +49 040 42 83 84 82 7 > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum -- ******************************************************* Ilya Ryabinkin Postdoctoral Scholar Physical and Environmental Sciences University of Toronto Scarborough http://www.utsc.utoronto.ca/~aizmaylov/Members.html ******************************************************* _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
