<div dir="ltr">Dear all,<div>I am running NVT MD with Quickstep on a box of water with 64 molecules. If I replace a water molecule with a KCl ion pair, i observe that the MD and SCF step times more than double on my setup. (MD from ~20 sec to ~46 sec). SCF iterations are converging (except the very first MD step) in around 30 steps in both cases but each SCF now takes over twice as long as before. Is there an explanation of why such a 'small' change in system could double the run time? Is KCl really so heavy to calculate compared to H2O? The number of electrons in the system increases by 8, from 512 to 520. Below my KCl input file. </div><div><br></div><div>Greetings,</div><div>Simiam</div><div><br></div><div><br></div><div><div><br></div><div>&GLOBAL</div><div><br></div><div> PROJECT H2O_KCl</div><div> RUN_TYPE MD</div><div> PRINT_LEVEL MEDIUM</div><div><br></div><div>&END GLOBAL</div><div><br></div><div>&FORCE_EVAL</div><div><br></div><div> METHOD Quickstep<span class="Apple-tab-span" style="white-space:pre"> </span>! GPW method.</div><div><br></div><div> &SUBSYS ! A subsystem: coordinates, topology, molecules and cell.</div><div><br></div><div> &CELL ! Supercell setup.</div><div> ABC [angstrom] 12.414 12.414 12.414<span class="Apple-tab-span" style="white-space:pre"> </span>! Using 64 H2O molecules, we thus get a density of 1g/cm^3.</div><div> PERIODIC XYZ <span class="Apple-tab-span" style="white-space:pre"> </span>! Use PBC in all dimensions.</div><div> &END CELL</div><div><br></div><div> &COORD</div><div> UNIT angstrom</div><div>H -0.567712 -0.469646 -0.645913</div><div>H 0.626116 -0.687796 0.308193</div><div>O 0 0 0</div><div>(...)</div><div>K 2.1035 2.1035 4.2735</div><div>Cl 4.1035 4.1035 2.6035 ###</div><div>H 3.73881 3.10388 5.46104<br></div><div>H 3.65742 2.89924 6.989</div><div>O 3.1035 3.1035 6.207</div><div>(...)</div><div> &END COORD</div><div><br></div><div> &KIND O</div><div> BASIS_SET DZVP-MOLOPT-GTH-q6</div><div> POTENTIAL GTH-PBE-q6</div><div> &END KIND</div><div> &KIND H</div><div> BASIS_SET DZVP-MOLOPT-GTH-q1</div><div> POTENTIAL GTH-PBE-q1</div><div> &END KIND</div><div> &KIND K</div><div> BASIS_SET DZVP-MOLOPT-SR-GTH-q9</div><div> POTENTIAL GTH-PBE-q9</div><div> &END KIND</div><div> &KIND Cl</div><div> BASIS_SET DZVP-MOLOPT-GTH-q7</div><div> POTENTIAL GTH-PBE-q7</div><div> &END KIND</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div> &END SUBSYS</div><div><br></div><div> &DFT</div><div><br></div><div> BASIS_SET_FILE_NAME BASIS_MOLOPT</div><div> POTENTIAL_FILE_NAME GTH_POTENTIALS</div><div> </div><div>! SPIN_POLARIZED<span class="Apple-tab-span" style="white-space:pre"> </span>! Do spin-polarized calculation</div><div><br></div><div> &POISSON</div><div> PERIODIC XYZ</div><div> &END POISSON</div><div><br></div><div> &QS</div><div> METHOD GPW</div><div> EPS_DEFAULT 1.0E-10 ! Set various epsilons for QS to values that will lead</div><div> <span class="Apple-tab-span" style="white-space:pre"> </span> <span class="Apple-tab-span" style="white-space:pre"> </span> ! to energy correct up to 1e-10.</div><div> &END QS</div><div><br></div><div> &MGRID</div><div> CUTOFF 400 ! This is Ecut of eq. 39 in VandeVondele (2005), i.e., plane-wave cutoff</div><div> <span class="Apple-tab-span" style="white-space:pre"> </span> <span class="Apple-tab-span" style="white-space:pre"> </span> ! that determines size of finest grid (see caption of Fig. 1). Cutoffs for</div><div><span class="Apple-tab-span" style="white-space:pre"> </span> ! the subsequent, coarser grid levels are given by eq. 39.</div><div> NGRIDS 4 ! This is N of eq. 39 in VandeVondele (2005), i.e., number of grids used.</div><div> REL_CUTOFF 40 ! This controls the grid level onto which Gaussians will be mapped.</div><div> &END MGRID</div><div><br></div><div> &XC</div><div><br></div><div> &XC_FUNCTIONAL</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&PBE</div><div> <span class="Apple-tab-span" style="white-space:pre"> </span> PARAMETRIZATION ORIG</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&END PBE</div><div> &END XC_FUNCTIONAL</div><div><br></div><div> &VDW_POTENTIAL</div><div><br></div><div> POTENTIAL_TYPE PAIR_POTENTIAL</div><div><br></div><div> &PAIR_POTENTIAL</div><div> TYPE DFTD3</div><div> REFERENCE_FUNCTIONAL PBE</div><div> CALCULATE_C9_TERM .TRUE.</div><div> PARAMETER_FILE_NAME dftd3.dat</div><div> R_CUTOFF 15.0</div><div> &END PAIR_POTENTIAL</div><div><br></div><div> &END VDW_POTENTIAL</div><div><br></div><div> &END XC</div><div><br></div><div> &SCF</div><div><br></div><div> SCF_GUESS RESTART<span class="Apple-tab-span" style="white-space:pre"> </span>! Use data from previous run as initial guess for wavefunction.</div><div> EPS_SCF 1.0E-6<span class="Apple-tab-span" style="white-space:pre"> </span>! Threshold for converged total energy.</div><div> MAX_SCF 300<span class="Apple-tab-span" style="white-space:pre"> </span>! Maximum number of SCF iterations performed.</div><div><br></div><div> &OT</div><div> PRECONDITIONER NONE<span class="Apple-tab-span" style="white-space:pre"> </span>! This should be stable with respect to the "Cholesky errors"</div><div> &END OT</div><div><br></div><div> &PRINT</div><div><span class="Apple-tab-span" style="white-space:pre"> </span> &RESTART ON</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>BACKUP_COPIES 1</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span> <span class="Apple-tab-span" style="white-space:pre"> </span>&EACH</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>MD 1</div><div> <span class="Apple-tab-span" style="white-space:pre"> </span> &END EACH</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>ADD_LAST NUMERIC</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span> &END RESTART</div><div><br></div><div> &END PRINT</div><div><br></div><div> &END SCF</div><div><br></div><div> &PRINT</div><div> &E_DENSITY_CUBE</div><div><br></div><div> STRIDE 1 1 1</div><div><br></div><div> &EACH </div><div><span class="Apple-tab-span" style="white-space:pre"> </span>MD 99999999</div><div> &END EACH</div><div><br></div><div> ADD_LAST NUMERIC</div><div> &END E_DENSITY_CUBE</div><div><br></div><div> &PDOS</div><div> COMPONENTS .FALSE.</div><div> NLUMO = -1</div><div> FILENAME dosfile</div><div> LOG_PRINT_KEY TRUE</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span> &EACH</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>MD 99999999</div><div><span class="Apple-tab-span" style="white-space:pre"> </span> &END EACH</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span> ADD_LAST NUMERIC</div><div> &END PDOS</div><div><br></div><div> &END PRINT</div><div><br></div><div> &END DFT</div><div><br></div><div>&END FORCE_EVAL</div><div><br></div><div>&MOTION</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&MD</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>ENSEMBLE<span class="Apple-tab-span" style="white-space:pre"> </span>NVT</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>STEPS<span class="Apple-tab-span" style="white-space:pre"> </span>10000</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>TEMPERATURE<span class="Apple-tab-span" style="white-space:pre"> </span>300.0<span class="Apple-tab-span" style="white-space:pre"> </span>! K</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>TIMESTEP<span class="Apple-tab-span" style="white-space:pre"> </span>0.5<span class="Apple-tab-span" style="white-space:pre"> </span>! fs</div><div><span class="Apple-tab-span" style="white-space:pre"> </span></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&THERMOSTAT</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>REGION GLOBAL</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>TYPE NOSE</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&NOSE</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>LENGTH 3<span class="Apple-tab-span" style="white-space:pre"> </span>! Length of Nose-Hoover chain</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>TIMECON 20.0<span class="Apple-tab-span" style="white-space:pre"> </span>! Period of typical vibrational motion in system in fs</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&END NOSE<span class="Apple-tab-span" style="white-space:pre"> </span></div><div><span class="Apple-tab-span" style="white-space:pre"> </span></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&END THERMOSTAT</div><div><span class="Apple-tab-span" style="white-space:pre"> </span></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&END MD</div><div><br></div><div> &PRINT</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&RESTART</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&EACH</div><div><span class="Apple-tab-span" style="white-space:pre"> </span> MD 1</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&END EACH</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>ADD_LAST NUMERIC</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>&END RESTART</div><div><br></div><div> &TRAJECTORY ON</div><div> ADD_LAST NUMERIC</div><div> FILENAME trajectory</div><div> &END TRAJECTORY</div><div><br></div><div> &END PRINT</div><div><br></div><div>&END MOTION</div></div><div><br></div><div><br></div></div>