<div dir="ltr"><div>Hi,</div><div> </div><div>The tutorial works because it is a simple case with small exponents in the basis set. If you have an element (or especially cation) with large exponents in the basis set, you need to use a higher cutoff. The CUTOFF should be at least as large as the largest exponent in your basis set multiplied by the REL_CUTOFF. Then round up to a nice number to report in the paper, nearest 10, 20, 50, or 100 are common. Na, Mg, H, and O are common elements to base your cutoff on.</div><div> </div><div><div style="background-color: rgb(250, 250, 250); border-color: rgb(187, 187, 187); border-style: solid; border-width: 1px; overflow-wrap: break-word;" class="prettyprint"><code class="prettyprint"><div class="subprettyprint">Na DZVP-GTH-q9 DZVP-GTH 2 2 0 1 6 3 2 17.6698382207 -0.1362364777 0.0270957219 0.0000000000 0.0791980974 0.0000000000 6.9070658063 -0.0645835666 0.0098734119 0.0000000000 0.2184139257 0.0000000000 2.6098601451 0.3866153961 -0.0737170396 0.0000000000 0.3764887364 0.0000000000 0.9649548796 0.5971358883 -0.2186742776 0.0000000000 0.3922304007 0.0000000000 0.3400348369 0.1756697026 -0.0301066303 0.0000000000 0.1808407220 0.0000000000 0.0432486046 -0.0017104621 1.0388865857 1.0000000000 0.0057696324 1.0000000000 3 2 2 1 1 0.0973000000 1.0000000000 </div></code></div></div><div> </div><div>In my experience, REL_CUTOFF=50 Ry is a good choice for static cell calculations and REL_CUTOFF=80 Ry is a good choice for dynamic cell calculations. Both figures are based on experience with condensed phase simulation. This leads to CUTOFFs of ~600 Ry and ~1000 Ry for liquid water for NVT and NPT simulations, respectively. The devs had a recent paper on accurate simulations of liquid water which draws similar conclusions when not using smoothing. </div><div> </div><div>-T</div><div> </div> On Thursday, October 10, 2019 at 8:13:29 AM UTC-3, Akshay Malik wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir="ltr"><div>Dear all,</div><div>I am trying to do cutoff-convergence for my system but it is only converging up to two digits after the decimal point.</div><div>Please suggest some method by which I can get converged energy up to 6 decimals. </div><div> </div><div># Grid cutoff vs total energy</div># Date: Thu Oct 10 16:37:32 IST 2019 # PWD: /home/space/cp2k/cutoff-convergence # REL_CUTOFF = 60 # Cutoff (Ry) | Total Energy (Ha) | NG on grid 1 | NG on grid 2 | NG on grid 3 | NG on grid 4 50.00 -1337.8915343935 668903 50882 240 0 100.00 -1351.0266889654 1216132 286203 11290 0 150.00 -1351.6349634609 1071797 364690 75938 1200 200.00 -1351.6825629692 975942 418150 115933 3600 250.00 -1351.6992612267 875755 439820 192650 5400 300.00 -1351.6990099247 791971 424161 286203 11290 350.00 -1351.6961310939 735698 431201 323555 23171 400.00 -1351.6944391280 687700 428173 341928 55824 450.00 -1351.6933108152 644645 427152 364690 77138 <div> 500.00 -1351.6931016574 603223 441589 368145 100668</div><div> </div><div><div>I am using this cp2k file section for calculating energy:</div><div>&FORCE_EVAL METHOD Quickstep &DFT BASIS_SET_FILE_NAME GTH_BASIS_SETS POTENTIAL_FILE_NAME GTH_POTENTIALS &MGRID NGRIDS 4 CUTOFF LT_cutoff REL_CUTOFF LT_rel_cutoff &END MGRID &QS EPS_DEFAULT 1.0E-10 &END QS &SCF SCF_GUESS ATOMIC EPS_SCF 1.0E-6 MAX_SCF 1 ADDED_MOS 10 CHOLESKY INVERSE &SMEAR ON METHOD FERMI_DIRAC ELECTRONIC_TEMPERATURE [K] 333 &END SMEAR &DIAGONALIZATION ALGORITHM STANDARD &END DIAGONALIZATION &MIXING METHOD BROYDEN_MIXING ALPHA 0.4 BETA 0.5 NBROYDEN 8 &END MIXING &END SCF &XC &XC_FUNCTIONAL BLYP &END &END &END DFT</div></div><div> </div></div> </blockquote></div>