Dear CP2k users and developers,<div><br></div><div>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.</div><div><br></div><div>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.</div><div><br></div><div>It is worth noting this is a hexagonal cell and force error is primarily on the z direction. Input file is enclosed.</div><div><br></div><div>Thanks, Wei</div><div><br></div><div><img alt="Graph2.png" data-iml="4693074.869999996" width="534px" height="412px" src="cid:9226a54f-6f30-4f26-b5c2-e27216df9f83"><br></div><div><br></div><div><br></div><div><div>&GLOBAL</div><div> PROJECT SiC</div><div> RUN_TYPE ENERGY_FORCE</div><div> PRINT_LEVEL LOW</div><div>&END GLOBAL</div><div>&FORCE_EVAL</div><div> STRESS_TENSOR ANALYTICAL</div><div> METHOD QS</div><div> &DFT</div><div> BASIS_SET_FILE_NAME BASIS_MOLOPT</div><div> POTENTIAL_FILE_NAME GTH_POTENTIALS</div><div> </div><div> &MGRID</div><div> CUTOFF 400</div><div> REL_CUTOFF 60</div><div> &END MGRID</div><div><br></div><div> &QS</div><div> METHOD GPW</div><div> EPS_DEFAULT 1.0E-12</div><div> &END QS</div><div> </div><div> &SCF </div><div> SCF_GUESS ATOMIC</div><div> MAX_SCF 100</div><div> EPS_SCF 5.0E-8</div><div> ADDED_MOS 60</div><div> CHOLESKY INVERSE</div><div> &SMEAR ON</div><div> METHOD FERMI_DIRAC</div><div> ELECTRONIC_TEMPERATURE [K] 300</div><div> &END SMEAR</div><div> &DIAGONALIZATION</div><div> &END DIAGONALIZATION</div><div> &MIXING</div><div> METHOD BROYDEN_MIXING</div><div> ALPHA 0.2</div><div> &END </div><div> &PRINT</div><div> &RESTART OFF</div><div> &END</div><div> &END</div><div> &END SCF</div><div> </div><div> &XC</div><div> &XC_FUNCTIONAL PBE</div><div> &END XC_FUNCTIONAL</div><div> &END XC</div><div> </div><div> &POISSON</div><div> PERIODIC XYZ</div><div> &END</div><div><br></div><div> &PRINT</div><div> &E_DENSITY_CUBE OFF</div><div> &EACH</div><div> MD 10</div><div> &END EACH</div><div> STRIDE 1 1 1 </div><div> &END E_DENSITY_CUBE</div><div> &END PRINT</div><div> &END DFT</div><div> </div><div> &SUBSYS</div><div> &KIND Si</div><div> ELEMENT Si</div><div> BASIS_SET DZVP-MOLOPT-SR-GTH</div><div> POTENTIAL GTH-PBE</div><div> &END KIND</div><div> &KIND C</div><div> ELEMENT C</div><div> BASIS_SET DZVP-MOLOPT-SR-GTH</div><div> POTENTIAL GTH-PBE</div><div> &END KIND </div><div> &CELL</div><div> PERIODIC XYZ</div><div> A 9.2430000305 0.0000000000 0.0000000000</div><div> B -4.6215010811 8.0046722182 0.0000000000</div><div> C 0.0000000000 0.0000000000 15.1247997284</div><div> &END CELL</div><div><br></div><div> &COORD</div><div>Si 0.0 0.0 0.0</div><div>Si -1.5405004 2.6682241 0.0</div><div>Si -3.0810008 5.3364482 0.0</div><div>Si 3.0810001 0.0 0.0</div><div>Si 1.5404997 2.6682241 0.0</div><div>Si -7.1525574e-07 5.3364482 0.0</div><div>Si 6.1620002 0.0 0.0</div><div>Si 4.6215 2.6682241 0.0</div><div>Si 3.0809994 5.3364482 0.0</div><div>Si 0.0 0.0 7.5623999</div><div>Si -1.5405004 2.6682241 7.5623999</div><div>Si -3.0810008 5.3364482 7.5623999</div><div>Si 3.0810001 0.0 7.5623999</div><div>Si 1.5404997 2.6682241 7.5623999</div><div>Si -7.1525574e-07 5.3364482 7.5623999</div><div>Si 6.1620002 0.0 7.5623999</div><div>Si 4.6215 2.6682241 7.5623999</div><div>Si 3.0809994 5.3364482 7.5623999</div><div>Si -1.1920929e-07 1.7788159 2.5208001</div><div>Si -1.5405003 4.4470396 2.5208001</div><div>Si -3.0810008 7.1152635 2.5208001</div><div>Si 3.0810001 1.7788159 2.5208001</div><div>Si 1.5405 4.4470396 2.5208001</div><div>Si -4.7683716e-07 7.1152635 2.5208001</div><div>Si 6.1619997 1.7788159 2.5208001</div><div>Si 4.6215 4.4470396 2.5208001</div><div>Si 3.0809994 7.1152635 2.5208001</div><div>Si 1.5405 0.889408 10.0832005</div><div>Si -4.7683716e-07 3.5576318 10.0832005</div><div>Si -1.5405007 6.2258563 10.0832005</div><div>Si 4.6215 0.889408 10.0832005</div><div>Si 3.0809999 3.5576318 10.0832005</div><div>Si 1.5404995 6.2258563 10.0832005</div><div>Si 7.7025004 0.889408 10.0832005</div><div>Si 6.1620002 3.5576318 10.0832005</div><div>Si 4.621501 6.2258563 10.0832005</div><div>Si 1.5405001 0.889408 5.0350456</div><div>Si -2.3841858e-07 3.5576318 5.0350456</div><div>Si -1.5405004 6.2258563 5.0350456</div><div>Si 4.6215 0.889408 5.0350456</div><div>Si 3.0809999 3.5576318 5.0350456</div><div>Si 1.5404995 6.2258563 5.0350456</div><div>Si 7.7025004 0.889408 5.0350456</div><div>Si 6.1620002 3.5576318 5.0350456</div><div>Si 4.621501 6.2258563 5.0350456</div><div>Si -2.3841858e-07 1.7788158 12.5974455</div><div>Si -1.5405004 4.4470396 12.5974455</div><div>Si -3.0810008 7.1152635 12.5974455</div><div>Si 3.0810003 1.7788158 12.5974455</div><div>Si 1.5405 4.4470396 12.5974455</div><div>Si -4.7683716e-07 7.1152635 12.5974455</div><div>Si 6.1619997 1.7788158 12.5974455</div><div>Si 4.6215 4.4470396 12.5974455</div><div>Si 3.0809994 7.1152635 12.5974455</div><div>C -1.1920929e-07 1.7788159 0.6231418</div><div>C -1.5405003 4.4470396 0.6231418</div><div>C -3.0810008 7.1152635 0.6231418</div><div>C 3.0810001 1.7788159 0.6231418</div><div>C 1.5405 4.4470396 0.6231418</div><div>C -4.7683716e-07 7.1152635 0.6231418</div><div>C 6.1619997 1.7788159 0.6231418</div><div>C 4.6215 4.4470396 0.6231418</div><div>C 3.0809994 7.1152635 0.6231418</div><div>C 1.5405 0.889408 8.1855412</div><div>C -4.7683716e-07 3.5576318 8.1855412</div><div>C -1.5405007 6.2258563 8.1855412</div><div>C 4.6215 0.889408 8.1855412</div><div>C 3.0809999 3.5576318 8.1855412</div><div>C 1.5404995 6.2258563 8.1855412</div><div>C 7.7025004 0.889408 8.1855412</div><div>C 6.1620002 3.5576318 8.1855412</div><div>C 4.621501 6.2258563 8.1855412</div><div>C 1.5405001 0.889408 3.1459584</div><div>C -2.3841858e-07 3.5576318 3.1459584</div><div>C -1.5405004 6.2258563 3.1459584</div><div>C 4.6215 0.889408 3.1459584</div><div>C 3.0809999 3.5576318 3.1459584</div><div>C 1.5404995 6.2258563 3.1459584</div><div>C 7.7025004 0.889408 3.1459584</div><div>C 6.1620002 3.5576318 3.1459584</div><div>C 4.621501 6.2258563 3.1459584</div><div>C -2.3841858e-07 1.7788158 10.7083578</div><div>C -1.5405004 4.4470396 10.7083578</div><div>C -3.0810008 7.1152635 10.7083578</div><div>C 3.0810003 1.7788158 10.7083578</div><div>C 1.5405 4.4470396 10.7083578</div><div>C -4.7683716e-07 7.1152635 10.7083578</div><div>C 6.1619997 1.7788158 10.7083578</div><div>C 4.6215 4.4470396 10.7083578</div><div>C 3.0809994 7.1152635 10.7083578</div><div>C 0.0 0.0 5.6657501</div><div>C -1.5405004 2.6682241 5.6657501</div><div>C -3.0810008 5.3364482 5.6657501</div><div>C 3.0810001 0.0 5.6657501</div><div>C 1.5404997 2.6682241 5.6657501</div><div>C -7.1525574e-07 5.3364482 5.6657501</div><div>C 6.1620002 0.0 5.6657501</div><div>C 4.6215 2.6682241 5.6657501</div><div>C 3.0809994 5.3364482 5.6657501</div><div>C 0.0 0.0 13.2281494</div><div>C -1.5405004 2.6682241 13.2281494</div><div>C -3.0810008 5.3364482 13.2281494</div><div>C 3.0810001 0.0 13.2281494</div><div>C 1.5404997 2.6682241 13.2281494</div><div>C -7.1525574e-07 5.3364482 13.2281494</div><div>C 6.1620002 0.0 13.2281494</div><div>C 4.6215 2.6682241 13.2281494</div><div>C 3.0809994 5.3364482 13.2281494</div><div> &END COORD</div><div> &END SUBSYS</div><div> </div><div> &PRINT</div><div> &FORCES ON</div><div> &END FORCES</div><div> &TOTAL_NUMBERS ON</div><div> &END TOTAL_NUMBERS</div><div> &END PRINT</div><div> </div><div>&END FORCE_EVAL</div><div><br></div></div>