<div dir="ltr">Dear Wei,<div><br></div><div>this drift indicates that you are not calculating forces accurately enough. You can see forces in the output file by adding <a href="https://manual.cp2k.org/cp2k-4_1-branch/CP2K_INPUT/FORCE_EVAL/PRINT/FORCES.html">https://manual.cp2k.org/cp2k-4_1-branch/CP2K_INPUT/FORCE_EVAL/PRINT/FORCES.html</a></div><div><br></div><div>Possible solutions are:</div><div><br></div><div>(i) use the GAPW method (add METHOD GAPW in the &QS section) - might be slower</div><div>(ii) Increase the CUTOFF - try 600 or 800 ry, at some point GAPW might be better</div><div>(iii) Use smoothing on the XC function</div><div>(iv) just subtract the COM motion to remove the drift (<a href="https://manual.cp2k.org/cp2k-4_1-branch/CP2K_INPUT/MOTION/MD.html#list_COMVEL_TOL">https://manual.cp2k.org/cp2k-4_1-branch/CP2K_INPUT/MOTION/MD.html#list_COMVEL_TOL</a>)<br><br>Matt<br><br>On Wednesday, January 4, 2017 at 1:29:39 AM UTC, Wei Lai wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir="ltr"><p class="MsoNormal" style="line-height:normal"><span style="font-size:10pt;font-family:Arial,sans-serif;background-image:initial;background-position:initial;background-repeat:initial">Dear cp2k users and developers,</span><span style="font-size:12.0pt;font-family:"Times New Roman",serif"></span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif"> </span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif">I am testing a NVE simulation with velocity scaling for crystalline CaO (300 K) and having questions regarding the drift of center of mass.</span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif"> </span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif">In a regular NVE simulation, I am expecting that (1) the simulation box is fixed and positions of atoms can be in fractional/scaled or Cartesian units, (2) if atoms moved out of the simulation box, they can be folded back to the box or left unchanged, (3) the mass-averaged position centers oscillate around x, y, z direction. I am showing the center of mass positions from VASP, which are consistent with the expectation.</span></p><p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif"><br></span></p><p style="text-align:center;clear:both"></p><p style="text-align:center;clear:both"><a href="https://lh3.googleusercontent.com/-tRDdhXVYalE/WGxP2ScXNBI/AAAAAAAAhnk/8bGLtoxRwxINxHoXywkIJFBPOkR4IipMwCLcB/s1600/cp2k-vs-VASP.TIF" style="margin-left:1em;margin-right:1em" target="_blank" rel="nofollow" onmousedown="this.href='https://lh3.googleusercontent.com/-tRDdhXVYalE/WGxP2ScXNBI/AAAAAAAAhnk/8bGLtoxRwxINxHoXywkIJFBPOkR4IipMwCLcB/s1600/cp2k-vs-VASP.TIF';return true;" onclick="this.href='https://lh3.googleusercontent.com/-tRDdhXVYalE/WGxP2ScXNBI/AAAAAAAAhnk/8bGLtoxRwxINxHoXywkIJFBPOkR4IipMwCLcB/s1600/cp2k-vs-VASP.TIF';return true;"><img src="https://lh3.googleusercontent.com/-tRDdhXVYalE/WGxP2ScXNBI/AAAAAAAAhnk/8bGLtoxRwxINxHoXywkIJFBPOkR4IipMwCLcB/s400/cp2k-vs-VASP.TIF" border="0" width="400" height="170"></a></p><p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif"><br></span></p><p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif"><br></span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif"> </span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif">If I do the same for cp2k (input file enclosed), I am clearly seeing drift of center of mass. If I analyze the dynamics of the trajectory (now shown), it appears that both Ca and O atoms are diffusing instead of vibrating, as obtained from VASP trajectory.</span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif"> </span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif">I am wondering if you have seen similar behaviors or if I have the wrong settings in the input file.</span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif"> </span></p> <p class="MsoNormal" style="margin-bottom:0.0001pt;line-height:normal;background-image:initial;background-position:initial;background-repeat:initial"><span style="font-size:10pt;font-family:Arial,sans-serif">Thanks, Wei</span></p></div></blockquote></div></div>