Hi all, <div><br></div><div>I am investigating a molecular liquid system, namely liquid-Se. It is formed of short chains of Se (down to only 2 Se atoms), which may show partially occupied electronic states, especially in the low pressure regime, in which molecules are well separated. I am slightly confused about how to model such a system using CP2K. </div><div><br></div><div>I have started running unrestricted Kohn-Sham MD calculations, starting from an amorphous configuration of Se8 molecules in a chain configuration. I do have an even number of electrons, but I am suspecting spin polarization due to the reasons mentioned above. I've been checking for spin contamination in the CP2K output, and obtained the following for the first 100 steps of dynamics: </div><div><br></div><div><div> <font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 -0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 -0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 -0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 -0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 -0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 -0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 -0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 -0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000000</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000002</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000018</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.000152</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.001315</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.012071</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 0.108839</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 1.570334</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 8.075949</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 12.475536</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.594641</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.297790</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.214178</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.323013</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.129883</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.688840</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.961233</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.596193</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.578972</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.859515</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.810544</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.870891</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.549977</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.490598</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.477700</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.251470</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.256963</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.245575</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.657994</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.097974</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.181373</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.265038</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.134708</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.176089</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.011084</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.038357</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.313602</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.458239</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.474756</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.064850</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.349064</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.697990</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.740888</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.605483</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.619671</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.146289</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.571982</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.791026</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.182009</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.201162</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.799011</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 17.191503</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.657538</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.398196</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.685182</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 17.269278</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 17.420976</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 17.327620</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 17.123223</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 17.213689</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 17.264376</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 17.123970</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.758495</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.487501</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.738201</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.527679</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 16.042440</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.726199</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.538890</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.731163</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.596686</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.086832</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.170306</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.774768</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.358169</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.818519</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 15.032944</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.517417</font></div><div><font size="1" face="Courier New"> Ideal and single determinant S**2 : 0.000000 14.088642</font></div></div><div><font size="1" face="Courier New"><br></font></div><div>Should I be bothered? Over this short MD run, some Se8 chains already break into smaller chunks - so I'm expecting more singly-occupied electronic states than at the beginning. I'm having a hard time understanding the connection between spin polarization in the "isolated, single molecule" formalism of CP2K and spin polarization in condensed molecular systems. <br></div><div><br></div><div>One last question : any tips on accelerating SCF convergence of UKS related to the OT method? </div><div><br></div><div>thank you, </div><div>Tom</div><div><br></div><div><br></div>