<div dir="ltr">Dear CP2K users and experts.<div><br><div>I am trying to simulate the interaction of a surface with a liquid layer under a high pressure using ab initio molecular dynamics. The system is illustrated in the figure below (I have some specific reasons that I need to use vacuum). In order to apply the load to the top slab an external force acting on the layer is needed. </div><div><br></div><p class="separator" style="text-align: center; clear: both;"><img src="cid:d3270a66-0a6b-4c48-9e22-144b7cbc9f82" alt="Slide1.jpeg" width="258" height="320" style="margin-left: 1em; margin-right: 1em;"></p><div><br></div><div>I found in the tutorial by Prof. Marcella (<a href="https://www.cp2k.org/exercises:2015_cecam_tutorial:mtd1" target="_blank" rel="nofollow" style="cursor: pointer;">https://www.cp2k.org/<wbr>exercises:2015_cecam_tutorial:<wbr>mtd1</a>) using external potential (<b><a href="https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/EXTERNAL_POTENTIAL.html">CP2K_INPUT / FORCE_EVAL / EXTERNAL_POTENTIAL</a></b>) to constrain the motion of molecules. From my understanding the external potential will act on each atom with a force of F=-dE/dr. So my idea is using the command to setup a constant external force to the top atomic layers.</div><div><br></div><div><div class="prettyprint" style="background-color: rgb(250, 250, 250); border-color: rgb(187, 187, 187); border-style: solid; border-width: 1px; overflow-wrap: break-word;"><code class="prettyprint"><div class="subprettyprint"><span style="color: #660;" class="styled-by-prettify">&</span><span style="color: #000;" class="styled-by-prettify">EXTERNAL_POTENTIAL<br></span><font color="#000000"><span style="color: #000;" class="styled-by-prettify">      ATOMS_LIST   </span><span style="color: #066;" class="styled-by-prettify">1.</span><span style="color: #660;" class="styled-by-prettify">.</span><span style="color: #066;" class="styled-by-prettify">20</span></font><span style="color: #000;" class="styled-by-prettify"><br></span><font color="#000000"><span style="color: #000;" class="styled-by-prettify">      FUNCTION </span></font><span style="color: #660;" class="styled-by-prettify">(</span><span style="color: #000;" class="styled-by-prettify">A</span><span style="color: #660;" class="styled-by-prettify">/</span><span style="color: #000;" class="styled-by-prettify">B</span><span style="color: #660;" class="styled-by-prettify">)*</span><span style="color: #000;" class="styled-by-prettify">Z<br>      PARAMETERS A B<br>      UNITS </span><span style="color: #660;" class="styled-by-prettify">[</span><span style="color: #000;" class="styled-by-prettify">eV</span><span style="color: #660;" class="styled-by-prettify">]</span><span style="color: #000;" class="styled-by-prettify"> </span><span style="color: #660;" class="styled-by-prettify">[</span><span style="color: #000;" class="styled-by-prettify">angstrom</span><span style="color: #660;" class="styled-by-prettify">]</span><span style="color: #000;" class="styled-by-prettify"><br>      VALUES </span><span style="color: #066;" class="styled-by-prettify">0.5</span><span style="color: #000;" class="styled-by-prettify"> </span><span style="color: #066;" class="styled-by-prettify">1.0</span><span style="color: #000;" class="styled-by-prettify"><br></span><span style="color: #660;" class="styled-by-prettify">&</span><span style="color: #008;" class="styled-by-prettify">END</span><span style="color: #000;" class="styled-by-prettify"> EXTERNAL_POTENTIAL<br></span></div></code></div><br>That would applied a constant normal (along z direction) force of 0.5 eV/A (this value is chosen randomly) to the chosen atoms. I wonder if the above setting will work?</div></div><div><br></div><div>Please correct me if I have some misunderstanding. </div><div>I appreciate any advises and recommendations.</div><div><br></div><div>Regards</div><div>Nam</div></div>