<div dir="ltr">Matt,<div><br></div><div>Thanks for the suggestions. Examining the force noise suggests that higher cutoff values are needed. Increasing the cutoff values does stabilize the center of mass, although the statistics of fluctuation are different from those from VASP. But I guess this is probably due to different types of basis sets.</div><div><br></div><div>Wei<br><br>On Thursday, January 5, 2017 at 10:21:24 AM UTC-5, Matt W wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><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" target="_blank" rel="nofollow" onmousedown="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Fcp2k-4_1-branch%2FCP2K_INPUT%2FFORCE_EVAL%2FPRINT%2FFORCES.html\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNFaLygzb8FuDLdi14y3ugcP3kEsrw';return true;" onclick="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Fcp2k-4_1-branch%2FCP2K_INPUT%2FFORCE_EVAL%2FPRINT%2FFORCES.html\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNFaLygzb8FuDLdi14y3ugcP3kEsrw';return true;">https://manual.cp2k.<wbr>org/cp2k-4_1-branch/CP2K_<wbr>INPUT/FORCE_EVAL/PRINT/FORCES.<wbr>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" target="_blank" rel="nofollow" onmousedown="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Fcp2k-4_1-branch%2FCP2K_INPUT%2FMOTION%2FMD.html%23list_COMVEL_TOL\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNEla95swqaUuWbMqhASs3MzvYw-Ng';return true;" onclick="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Fcp2k-4_1-branch%2FCP2K_INPUT%2FMOTION%2FMD.html%23list_COMVEL_TOL\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNEla95swqaUuWbMqhASs3MzvYw-Ng';return true;">https://manual.cp2k.org/cp2k-<wbr>4_1-branch/CP2K_INPUT/MOTION/<wbr>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" rel="nofollow" target="_blank" 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></blockquote></div></div>