<div dir="ltr">Dear Prof. Thomas Kühne,<div><br></div><div>By relaxing the cell do you meaning doing a CELL_OPT operation? Or doing NPT simulations? Could you please elaborate on that?</div><div><br></div><div>And here's my D3 correction and SCF section: </div><div><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &SCF</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> SCF_GUESS ATOMIC ! can be used to RESTART an interrupted calculation</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> MAX_SCF 30</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> EPS_SCF 1.0E-6 ! accuracy of the SCF procedure typically 1.0E-6 - 1.0E-7</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &OT</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> ! an accurate preconditioner suitable also for larger systems</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> PRECONDITIONER FULL_SINGLE_INVERSE</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> ! the most robust choice (DIIS might sometimes be faster, but not as stable).</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> MINIMIZER DIIS</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &END OT</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &OUTER_SCF ! repeat the inner SCF cycle 10 times</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> MAX_SCF 10</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> EPS_SCF 1.0E-6 ! must match the above</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &END</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><br></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &PRINT</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &RESTART OFF</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &END</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &END</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &END SCF</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0); min-height: 19px;"><span style="font-variant-ligatures: no-common-ligatures;"></span><br></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> ! specify the exchange and correlation treatment</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &XC</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> </span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &XC_FUNCTIONAL BLYP</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &END XC_FUNCTIONAL</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> ! adding Grimme's D3 correction (by default without C9 terms)</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &VDW_POTENTIAL</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> POTENTIAL_TYPE PAIR_POTENTIAL</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &PAIR_POTENTIAL</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> PARAMETER_FILE_NAME dftd3.dat</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> TYPE DFTD3</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> REFERENCE_FUNCTIONAL BLYP</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> R_CUTOFF [angstrom] 11.00</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &END</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &END VDW_POTENTIAL</span></p><p style="font-stretch: normal; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"> &END XC</span></p><div><span style="font-variant-ligatures: no-common-ligatures;"><br></span></div><div><span style="font-variant-ligatures: no-common-ligatures;"><br></span></div><div><span style="font-variant-ligatures: no-common-ligatures;">Thanks,</span></div><div><span style="font-variant-ligatures: no-common-ligatures;">Ramanish Singh</span></div><div><span style="font-variant-ligatures: no-common-ligatures;"><br></span></div><div><span style="font-variant-ligatures: no-common-ligatures;"><br></span></div>On Thursday, September 26, 2019 at 3:50:14 AM UTC-5, tkuehne wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div style="word-wrap:break-word">Dear Ramanish Singh, <div><br></div><div>if I would know the answer I wouldn’t do any calculations anymore, but rather use intuition instead ;) </div><div>However, I GUESS that your observation is not due to phase coexistence (I have a lot to say here, </div><div>but would be way beyond the purpose of this mailing list), but more due to an underestimation of the </div><div>density by DFT. Are you using any form of dispersion correction? Long story short, beside the usage </div><div>of vdW correction, I recommend to relax the cell instead of over pressurizing it. </div><div><br></div><div>Best, </div><div>Thomas Kühne</div><div><br><div><blockquote type="cite"><div>Am 24.09.2019 um 16:27 schrieb Ramanish Singh <<a href="javascript:" target="_blank" gdf-obfuscated-mailto="TpNmI3GpCAAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;">si...@umn.edu</a>>:</div><br><div><div dir="ltr">Thanks Thomas Kühne. <div>I am simulating liquid Iodine close to the Vapor Liquid coexistence curve using BLYP functional. I used experimental density to find the V for my NVT simulations. But now I suspect there can be a two phase system in my box and that's why the pressure is becoming negative. </div><div>So instead of the experimental density I am using slightly higher density(~10 percent higher) to make sure it is in the liquid phase at that Temperature. What are your thoughts on this?</div><div><br></div><div>Thanks,</div><div>Ramanish Singh<br><br>On Monday, September 23, 2019 at 12:59:41 PM UTC-5, tkuehne wrote:<blockquote class="gmail_quote" style="margin:0;margin-left:0.8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">Dear Ramanish Singh, <div><br></div><div>minimal mispredictions within lattice constant and vectors </div><div>may entail large changes in the pressure. So observing a </div><div>rather large negative pressure is not necessarily indicative </div><div>of a problem. Beside that the usage of good basis sets and </div><div>tight SCF convergence is essential, it is hard to say anything </div><div>specific without detailed knowledge on what you plan to do. </div><div><br></div><div>Best, </div><div>Thomas Kühne</div><div><br><div><div><blockquote type="cite"><div>Am 23.09.2019 um 18:01 schrieb Ramanish Singh <<a rel="nofollow">si...@umn.edu</a>>:</div><br><div><div dir="ltr">Hi,<div><br></div><div>I am simulating a system of Iodine atoms using BLYP functional in the NVT ensemble.</div><div>But when I am calculating the pressure, using STRESS_TENSOR ANALYTICAL in the FORCE_EVAL section, my pressure (average of the xx,yy and zz elements) is coming out to be negative which is far from the experimental pressure at that density and Temperature. </div><div>I can not figure out why this is happening. </div><div><br></div><div>Thanks,</div><div>Ramanish Singh</div></div><div><br></div>
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