<div dir="ltr">Dear Ning, <div><br></div><div>It is a very simple potential, which is zero at the center of the Cartesian system, and grows as a power 4 of the square of the atomic coordinates, with a very small prefactor.</div><div> Just plot it to see how it grows and in which range it is negligibly small.</div><div>This definition assumes that the molecular system is centred at 0, and it is not extending beyond the range where the potential is still negligible.</div><div>Regards,</div><div>Marcella<br><br>On Monday, December 16, 2019 at 3:44:46 PM UTC+1, ning zhang wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir="ltr">Hi Everyone,<div><br></div><div>I am learning the metadynamics by the website: <a href="https://www.cp2k.org/exercises:2015_cecam_tutorial:mtd1" target="_blank" rel="nofollow" onmousedown="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fwww.cp2k.org%2Fexercises%3A2015_cecam_tutorial%3Amtd1\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNG758lQeebTcHKlVCuQXsO5W9meow';return true;" onclick="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fwww.cp2k.org%2Fexercises%3A2015_cecam_tutorial%3Amtd1\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNG758lQeebTcHKlVCuQXsO5W9meow';return true;">https://www.cp2k.org/<wbr>exercises:2015_cecam_tutorial:<wbr>mtd1</a></div><div><br></div><div>However, there is a question on the <a href="https://manual.cp2k.org/trunk/CP2K_INPUT.html" style="font-size:medium;font-family:monospace;text-transform:uppercase" target="_blank" rel="nofollow" onmousedown="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Ftrunk%2FCP2K_INPUT.html\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNGrhwIJKdGMVLw8iPdrQ9hT1Z19YA';return true;" onclick="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Ftrunk%2FCP2K_INPUT.html\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNGrhwIJKdGMVLw8iPdrQ9hT1Z19YA';return true;">CP2K_INPUT</a><span style="font-size:medium;color:rgb(0,0,0);font-family:monospace;text-transform:uppercase">/</span><a href="https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL.html" style="font-size:medium;font-family:monospace;text-transform:uppercase" target="_blank" rel="nofollow" onmousedown="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Ftrunk%2FCP2K_INPUT%2FFORCE_EVAL.html\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNHtFlOfSFz_75F23B93KEdPwyxK6g';return true;" onclick="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Ftrunk%2FCP2K_INPUT%2FFORCE_EVAL.html\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNHtFlOfSFz_75F23B93KEdPwyxK6g';return true;">FORCE_EVAL</a><span style="font-size:medium;color:rgb(0,0,0);font-family:monospace;text-transform:uppercase">/</span><a href="https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/EXTERNAL_POTENTIAL.html" style="font-size:medium;font-family:monospace;text-transform:uppercase" target="_blank" rel="nofollow" onmousedown="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Ftrunk%2FCP2K_INPUT%2FFORCE_EVAL%2FEXTERNAL_POTENTIAL.html\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNGzpu1Br4bP1pojYq4GTbHx-Ma6gw';return true;" onclick="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fmanual.cp2k.org%2Ftrunk%2FCP2K_INPUT%2FFORCE_EVAL%2FEXTERNAL_POTENTIAL.html\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNGzpu1Br4bP1pojYq4GTbHx-Ma6gw';return true;">EXTE<wbr>RNAL_POTENTIAL</a>. In the first task of tutorial, an example on the dynamics of two HNO3 molecules over a graphene sheet are considered. If a constraint is not added, it is observed that the two molecules very fast and expolre a large spece of configurations, being often far from each other and far from graphene. In order to restrict the exploration to region, it is necessary to limit the movement of the two molecules. To this purpose, an external potential defining a spherical potential centered on the center of the system coordinated is added. The potential is given as follows:</div><div><pre style="padding:0.7em 1em;font-family:Consolas,"Andale Mono WT","Andale Mono","Bitstream Vera Sans Mono","Nimbus Mono L",Monaco,"Courier New",monospace;font-size:14px;direction:ltr;background-color:rgb(251,250,249);color:rgb(51,51,51);border-radius:2px;overflow:auto;border-width:1px;border-style:solid;border-color:rgb(204,204,204)"> &EXTERNAL_POTENTIAL
     ATOMS_LIST   61..70
     FUNCTION   0.000000000001*(Z^2)^4
  &END

  &EXTERNAL_POTENTIAL
     ATOMS_LIST   61..70
     FUNCTION   0.0000000000001*(X^2)^4
  &END

  &EXTERNAL_POTENTIAL
     ATOMS_LIST   61..70
     FUNCTION   0.0000000000001*(Y^2)^4
  &END</pre></div><div><br></div><div>Question: How does work on such external_potential? i.e., How does such external_potential constaint the two HNO3 molecules to the vicinity of graphene?</div><div><br></div><div>Ning</div></div></blockquote></div></div>