<div dir="ltr"><div>Hi,</div><div><br></div><div>Firstly, your initial cell parameters should be the same as the structure you downloaded. You don't need vacuum to optimize the bulk. If you are trying to mimic having a larger grid, set a larger REF_CELL instead.</div><div><br></div>For cell optimization you need a large supercell or you need kpoints,<div><br></div>1) MULTIPLE_UNIT_CELL X Y Z in both &CELL and &TOPOLOGY sections<br>2) KPOINTS as below<br><br><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">DFT<br> </span><span style="color: #660;" class="styled-by-prettify">...</span><span style="color: #000;" class="styled-by-prettify"><br> </span><span style="color: #660;" class="styled-by-prettify">&</span><span style="color: #000;" class="styled-by-prettify">KPOINTS<br> </span><a href="https://manual.cp2k.org/cp2k-6_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/KPOINTS.html#list_FULL_GRID"><span style="color: #000;" class="styled-by-prettify">FULL_GRID</span></a><span style="color: #000;" class="styled-by-prettify"> T<br> </span><a href="https://manual.cp2k.org/cp2k-6_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/KPOINTS.html#list_SCHEME"><span style="color: #000;" class="styled-by-prettify">SCHEME</span></a><span style="color: #000;" class="styled-by-prettify"> MONKHORST</span><span style="color: #660;" class="styled-by-prettify">-</span><span style="color: #000;" class="styled-by-prettify">PACK X Y Z<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"> KPOINTS<br> </span><span style="color: #660;" class="styled-by-prettify">...</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"> DFT</span></div></code></div><div><br>EPS_DEFAULT 1.0E-8 is usually set smaller as well (default is 1e-10). The kpoint route should converge within just a handful of optimization steps, supposing your stopping criteria are comparable to VASP. Then generate your slab.<br></div><div><br></div><div><br></div><div>-T</div><div><br><br>On Wednesday, August 14, 2019 at 8:25:15 PM UTC-4, Hasan Al-Mahayni wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir="ltr">Hello all,<div><br></div><div>I am fairly new to cp2k so I believe this issue is easily resolvable. My end goal is calculating adsorption energy of different molecules on copper surfaces (slab). However, the first step I need to do is optimize the cell parameters of copper(cell size). I know from materials project site that it is 3.62126 Angstroms. That is the configuration I start with and is attached by the name of "<a href="http://copper.xyz" target="_blank" rel="nofollow" onmousedown="this.href='http://www.google.com/url?q\x3dhttp%3A%2F%2Fcopper.xyz\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNHf9SERQqffjEa9U8Yw-7d0xjTQNg';return true;" onclick="this.href='http://www.google.com/url?q\x3dhttp%3A%2F%2Fcopper.xyz\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNHf9SERQqffjEa9U8Yw-7d0xjTQNg';return true;">copper.xyz</a>". The problem I am having is that when I run cell optimization on this (input file is "copper.inp"), I get the wrong results as the cell size shrinks (I get 3.4A). I think this is because of the vacuum between the copper cell and the simulation cell. My question is, what is the right way to set up the input file and especially the &CELL part. I started off by making the A B C cell size 10 A bigger than 3.62A, but that gives me the wrong result. If the A B C cell size is too small, I get an error saying geometry is wrong. Also, maybe GEO_OPT would be a more appropriate run type... I tried making supercell 2x2x2, 3x3x3, and 4x4x4 while keeping ABC cell size 10 A bigger every time, and the result gets closer to 3.62 but this method is not ideal as the system gets bigger and bigger and the calculation is more computationally expensive. Any ideas?</div><div><br></div><div>Thanks,</div><div><br></div><div>Hasan.</div> </div></blockquote></div></div>