<div dir="ltr"><div>Dear <span class="gmail-il">CP2K</span> users,</div><div><br></div><div>I was trying to check the effect of D3 interactions on the energy, forces, and stress. So, I ran two CP2K(version 8.2) jobs (<span style="color:rgb(53,28,117)">RUN_TYPE ENERGY_FORCE</span>) with and without D3 correction and printed stress and forces using, <br></div><div><span style="color:rgb(53,28,117)"> &PRINT<br> &FORCES ON<br> FILENAME =forces<br> &END FORCES<br> &STRESS_TENSOR ON<br> FILENAME =stress<br> &END STRESS_TENSOR<br> &END PRINT</span></div><div><span style="color:rgb(53,28,117)"> STRESS_TENSOR ANALYTICAL</span></div><div><span style="color:rgb(53,28,117)"><br></span></div><div>and printed D3 output using,</div><div><span style="color:rgb(53,28,117)"> &vDW_POTENTIAL<br> POTENTIAL_TYPE PAIR_POTENTIAL<br> &PAIR_POTENTIAL<br> TYPE DFTD3<br> PARAMETER_FILE_NAME dftd3.dat<br> REFERENCE_FUNCTIONAL PBE<br> VERBOSE_OUTPUT .TRUE.<br> &PRINT_DFTD<br> FILENAME =VDWForces<br> &END PRINT_DFTD<br> &END PAIR_POTENTIAL<br> &END vDW_POTENTIAL</span></div><div><br></div><div>I obtained following energy values,<br></div><div>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>></div><div>with D3:</div><div></div><div><span style="color:rgb(56,118,29)"> Dispersion energy: -0.43391295044042<br> Total energy: -1822.59757123461372</span></div><div></div><div>without D3:</div><div></div><div><span style="color:rgb(56,118,29)"><font size="2">Total energy: -1822.16365828416315</font></span></div><div><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<</div><div></div><div>It shows that E_DFT+D3 = E_DFT + E_D3. Since forces are negative gradients of energy, so my expectation was F_DFT+D3 = F_DFT + F_D3.<br></div><div><br></div><div>I checked the files with forces and found following values:</div><div></div><div>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>></div><div>with D3:</div><div></div><div><span style="color:rgb(56,118,29)"> Dispersion Forces <br> Atom Kind Forces <br> 1 1 -0.00064625376145 -0.00178929821343 0.00063408272599<br> 2 1 -0.00010368151520 0.00098624399705 -0.00068002896134<br> 3 1 -0.00015900750143 0.00000043929734 0.00016150708715<br> 4 1 -0.00176730962009 0.00065208064208 -0.00062160173245</span></div><div>----------------------------------------------------</div><div><span style="color:rgb(56,118,29)"> ATOMIC FORCES in [a.u.]<br><br> # Atom Kind Element X Y Z<br> 1 1 C 0.00005291 0.00012528 -0.00005636<br> 2 1 C -0.00000900 -0.00001802 0.00002341<br> 3 1 C 0.00001580 0.00007087 -0.00002165<br> 4 1 C -0.00011523 0.00002219 -0.00005222</span></div><div><div><br></div><div>without D3:</div><div></div><div><span style="color:rgb(56,118,29)"> ATOMIC FORCES in [a.u.]<br><br> # Atom Kind Element X Y Z<br> 1 1 C -0.00059335 -0.00166402 0.00057772<br> 2 1 C -0.00011269 0.00096823 -0.00065662<br> 3 1 C -0.00014321 0.00007131 0.00013985<br> 4 1 C -0.00188254 0.00067427 -0.00067382</span></div><div></div><div><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<</div><div><br></div></div><div>From the printed forces, I found that (assuming printed dispersion forces are in a.u.) that F_DFT+D3 = F_DFT - F_D3 (e.g. F1x: 0.00005291 = -0.00059335 - (-0.00064625376145) ), which should not be the case and it should be F_DFT+D3 = F_DFT <a class="gmail_plusreply" id="plusReplyChip-3">+</a> F_D3. </div><div><br></div><div>Similarly, I checked the stress and got following values,<br></div><div>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><br></div><div>with D3:</div><div><span style="color:rgb(56,118,29)"> Stress Tensor (dispersion)<br> -0.302617856781 -0.301607753891E-04 0.414417744693E-03<br> -0.301607753891E-04 -0.301666150572 0.101523675983E-03<br> 0.414417744693E-03 0.101523675983E-03 -0.302011925451 <br> Tr(P)/3 : -0.30209864426787675 </span></div><div>----------------------------------------------------</div><div> <span style="color:rgb(56,118,29)">STRESS| Analytical stress tensor [GPa]<br> STRESS| x y z<br> STRESS| x 1.06013861421E-03 -2.63120964024E-05 -3.93224150664E-03<br> STRESS| y -2.63120964024E-05 1.25227540891E-02 1.45254611477E-04<br> STRESS| z -3.93224150664E-03 1.45254611477E-04 7.18280089554E-03<br> STRESS| 1/3 Trace 6.92189786629E-03</span></div><div><br></div><div>without D3:</div><div><span style="color:rgb(56,118,29)"> STRESS| Analytical stress tensor [GPa]<br> STRESS| x y z<br> STRESS| x 2.67537379581E-01 2.45931708730E-07 -4.29716685938E-03<br> STRESS| y 2.45931708730E-07 2.78161945635E-01 5.58511123164E-05<br> STRESS| z -4.29716685938E-03 5.58511123164E-05 2.73126455701E-01<br> STRESS| 1/3 Trace 2.72941926972E-01</span></div><div><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<</div><div>Assuming the dispersion stress in a.u., I got the following relation Stress_DFT+D3 (GPa) = Stress_DFT (GPa) + Stress_D3 (a.u.)*4359.74393 / volume (Angstrom^3), which seems fine. <br></div><div><br></div><div>So from output from CP2K, I got following relations:<br></div><div>E_DFT+D3 (a.u.) = E_DFT (a.u.) + E_D3 (a.u.)</div><div>F_DFT+D3 (a.u.) = F_DFT (a.u.) - F_D3 (a.u.) <br></div><div>Stress_DFT+D3 (GPa) = Stress_DFT (GPa) + Stress_D3 (a.u.)*4359.74393 / volume (Ang^3)</div><div><div><b><br></b></div><div>Could you please help me to understand why there is subtraction of the forces to obtain total (DFT+D3) forces?<br><br></div></div><div><div><font size="2">Many thanks ,<br></font></div><div></div><div><font size="2">Abhishek</font><font color="#888888"><br></font></div></div><div><br></div><div><br></div></div>
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