Dear Juerg,<div> </div><div>Thanks for your comments. They make sense. However, this does add complexity as we have to check the force error of the whole MD trajectory and then adjust the cutoff, if we want to be careful.</div><div> </div><div>Thanks, Wei </div><div class="gmail_quote"><div dir="auto" class="gmail_attr">On Thursday, March 18, 2021 at 12:23:24 PM UTC-4 jgh wrote: </div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Hi there are two sources of errors that could be relevant for this. 1) by changing the cutoff, the relative position of the atoms within the real space grids change. This then leads to a change of energy and forces. This has been discussed before here. 2) By default you are using multiple grids and by changing the cutoff, the change in accuracy is not linear but might jump at certain cutoffs. best regards Juerg Hutter -------------------------------------------------------------- Juerg Hutter Phone : <a href="tel:+41%2044%20635%2044%2091" value="+41446354491" target="_blank" rel="nofollow">++41 44 635 4491</a> Institut für Chemie C FAX : <a href="tel:+41%2044%20635%2068%2038" value="+41446356838" target="_blank" rel="nofollow">++41 44 635 6838</a> Universität Zürich E-mail: <a href data-email-masked rel="nofollow">h...@chem.uzh.ch</a> Winterthurerstrasse 190 CH-8057 Zürich, Switzerland --------------------------------------------------------------- -----<a href data-email-masked rel="nofollow">c...@googlegroups.com</a> wrote: ----- To: "cp2k" <<a href data-email-masked rel="nofollow">c...@googlegroups.com</a>> From: "W. Lai" Sent by: <a href data-email-masked rel="nofollow">c...@googlegroups.com</a> Date: 03/18/2021 03:11PM Subject: [CP2K:14965] odd force drift convergence with respect to density cutoff Dear CP2k users and developers, I am seeing odd behavior on how force drift(error) change as we change the density cutoff value (from 400 to 1600 Ry), for a model material of SiC-6H. I am using the 7.1 version and I changed the force error ("Sum of Atomic Forces") to eV/A. While it is subjective to consider what is an acceptable value for the force error (i.e. 0.01 or 0.001 eV/A), such oscillation really makes it a difficult task to choose the appropriate cutoff. It is worth noting this is a hexagonal cell and force error is primarily on the z direction. Input file is enclosed. Thanks, Wei &GLOBAL PROJECT SiC RUN_TYPE ENERGY_FORCE PRINT_LEVEL LOW &END GLOBAL &FORCE_EVAL STRESS_TENSOR ANALYTICAL METHOD QS &DFT BASIS_SET_FILE_NAME BASIS_MOLOPT POTENTIAL_FILE_NAME GTH_POTENTIALS &MGRID CUTOFF 400 REL_CUTOFF 60 &END MGRID &QS METHOD GPW EPS_DEFAULT 1.0E-12 &END QS &SCF SCF_GUESS ATOMIC MAX_SCF 100 EPS_SCF 5.0E-8 ADDED_MOS 60 CHOLESKY INVERSE &SMEAR ON METHOD FERMI_DIRAC ELECTRONIC_TEMPERATURE [K] 300 &END SMEAR &DIAGONALIZATION &END DIAGONALIZATION &MIXING METHOD BROYDEN_MIXING ALPHA 0.2 &END &PRINT &RESTART OFF &END &END &END SCF &XC &XC_FUNCTIONAL PBE &END XC_FUNCTIONAL &END XC &POISSON PERIODIC XYZ &END &PRINT &E_DENSITY_CUBE OFF &EACH MD 10 &END EACH STRIDE 1 1 1 &END E_DENSITY_CUBE &END PRINT &END DFT &SUBSYS &KIND Si ELEMENT Si BASIS_SET DZVP-MOLOPT-SR-GTH POTENTIAL GTH-PBE &END KIND &KIND C ELEMENT C BASIS_SET DZVP-MOLOPT-SR-GTH POTENTIAL GTH-PBE &END KIND &CELL PERIODIC XYZ A 9.2430000305 0.0000000000 0.0000000000 B -4.6215010811 8.0046722182 0.0000000000 C 0.0000000000 0.0000000000 15.1247997284 &END CELL &COORD Si 0.0 0.0 0.0 Si -1.5405004 2.6682241 0.0 Si -3.0810008 5.3364482 0.0 Si 3.0810001 0.0 0.0 Si 1.5404997 2.6682241 0.0 Si -7.1525574e-07 5.3364482 0.0 Si 6.1620002 0.0 0.0 Si 4.6215 2.6682241 0.0 Si 3.0809994 5.3364482 0.0 Si 0.0 0.0 7.5623999 Si -1.5405004 2.6682241 7.5623999 Si -3.0810008 5.3364482 7.5623999 Si 3.0810001 0.0 7.5623999 Si 1.5404997 2.6682241 7.5623999 Si -7.1525574e-07 5.3364482 7.5623999 Si 6.1620002 0.0 7.5623999 Si 4.6215 2.6682241 7.5623999 Si 3.0809994 5.3364482 7.5623999 Si -1.1920929e-07 1.7788159 2.5208001 Si -1.5405003 4.4470396 2.5208001 Si -3.0810008 7.1152635 2.5208001 Si 3.0810001 1.7788159 2.5208001 Si 1.5405 4.4470396 2.5208001 Si -4.7683716e-07 7.1152635 2.5208001 Si 6.1619997 1.7788159 2.5208001 Si 4.6215 4.4470396 2.5208001 Si 3.0809994 7.1152635 2.5208001 Si 1.5405 0.889408 10.0832005 Si -4.7683716e-07 3.5576318 10.0832005 Si -1.5405007 6.2258563 10.0832005 Si 4.6215 0.889408 10.0832005 Si 3.0809999 3.5576318 10.0832005 Si 1.5404995 6.2258563 10.0832005 Si 7.7025004 0.889408 10.0832005 Si 6.1620002 3.5576318 10.0832005 Si 4.621501 6.2258563 10.0832005 Si 1.5405001 0.889408 5.0350456 Si -2.3841858e-07 3.5576318 5.0350456 Si -1.5405004 6.2258563 5.0350456 Si 4.6215 0.889408 5.0350456 Si 3.0809999 3.5576318 5.0350456 Si 1.5404995 6.2258563 5.0350456 Si 7.7025004 0.889408 5.0350456 Si 6.1620002 3.5576318 5.0350456 Si 4.621501 6.2258563 5.0350456 Si -2.3841858e-07 1.7788158 12.5974455 Si -1.5405004 4.4470396 12.5974455 Si -3.0810008 7.1152635 12.5974455 Si 3.0810003 1.7788158 12.5974455 Si 1.5405 4.4470396 12.5974455 Si -4.7683716e-07 7.1152635 12.5974455 Si 6.1619997 1.7788158 12.5974455 Si 4.6215 4.4470396 12.5974455 Si 3.0809994 7.1152635 12.5974455 C -1.1920929e-07 1.7788159 0.6231418 C -1.5405003 4.4470396 0.6231418 C -3.0810008 7.1152635 0.6231418 C 3.0810001 1.7788159 0.6231418 C 1.5405 4.4470396 0.6231418 C -4.7683716e-07 7.1152635 0.6231418 C 6.1619997 1.7788159 0.6231418 C 4.6215 4.4470396 0.6231418 C 3.0809994 7.1152635 0.6231418 C 1.5405 0.889408 8.1855412 C -4.7683716e-07 3.5576318 8.1855412 C -1.5405007 6.2258563 8.1855412 C 4.6215 0.889408 8.1855412 C 3.0809999 3.5576318 8.1855412 C 1.5404995 6.2258563 8.1855412 C 7.7025004 0.889408 8.1855412 C 6.1620002 3.5576318 8.1855412 C 4.621501 6.2258563 8.1855412 C 1.5405001 0.889408 3.1459584 C -2.3841858e-07 3.5576318 3.1459584 C -1.5405004 6.2258563 3.1459584 C 4.6215 0.889408 3.1459584 C 3.0809999 3.5576318 3.1459584 C 1.5404995 6.2258563 3.1459584 C 7.7025004 0.889408 3.1459584 C 6.1620002 3.5576318 3.1459584 C 4.621501 6.2258563 3.1459584 C -2.3841858e-07 1.7788158 10.7083578 C -1.5405004 4.4470396 10.7083578 C -3.0810008 7.1152635 10.7083578 C 3.0810003 1.7788158 10.7083578 C 1.5405 4.4470396 10.7083578 C -4.7683716e-07 7.1152635 10.7083578 C 6.1619997 1.7788158 10.7083578 C 4.6215 4.4470396 10.7083578 C 3.0809994 7.1152635 10.7083578 C 0.0 0.0 5.6657501 C -1.5405004 2.6682241 5.6657501 C -3.0810008 5.3364482 5.6657501 C 3.0810001 0.0 5.6657501 C 1.5404997 2.6682241 5.6657501 C -7.1525574e-07 5.3364482 5.6657501 C 6.1620002 0.0 5.6657501 C 4.6215 2.6682241 5.6657501 C 3.0809994 5.3364482 5.6657501 C 0.0 0.0 13.2281494 C -1.5405004 2.6682241 13.2281494 C -3.0810008 5.3364482 13.2281494 C 3.0810001 0.0 13.2281494 C 1.5404997 2.6682241 13.2281494 C -7.1525574e-07 5.3364482 13.2281494 C 6.1620002 0.0 13.2281494 C 4.6215 2.6682241 13.2281494 C 3.0809994 5.3364482 13.2281494 &END COORD &END SUBSYS &PRINT &FORCES ON &END FORCES &TOTAL_NUMBERS ON &END TOTAL_NUMBERS &END PRINT &END FORCE_EVAL -- You received this message because you are subscribed to the Google Groups "cp2k" group. 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