<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dear Rui,<div><br></div><div><div><div>On 12 Aug, 2011, at 16:12, DONG Rui wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Hi, all,<br><br>I am doing MD calculation in QuantumEspresso, and have a question now...<br><br>here are some of the input list<br><b> &ions<br> ion_temperature = 'reduce-T',<br> tempw=10,<br> delta_t = 1,<br>
nraise=10,<br> pot_extrapolation='second-order',<br> wfc_extrapolation='second-order',<br> /<br></b> <br>But I found the rescaling works only when delta_t is a negative number, which is different from what the documentation tells me.<br></blockquote><div><br></div><div>In Doc/INPUT_PW.txt, I find the following lines:</div><div><br></div><div><div> Variable: ion_temperature</div><div><br></div><div> Type: CHARACTER</div><div><div><br></div><div> 'reduce-T' reduce ionic temperature every "nraise" steps</div><div> by the (negative) value "delta_t"</div><div><br></div><div>and</div><div><br></div><div><div> Variable: delta_t</div><div><br></div><div> Type: REAL</div></div><div><br></div><div><div> if ion_temperature='reduce-T':</div><div> every 'nraise' steps the instantaneous temperature is</div><div> reduced by -delta_T (.e. delta_t is added to the temperature)</div><div><br></div><div> The instantaneous temperature is calculated at the end of</div><div> every ionic move and BEFORE rescaling. This is the temperature</div><div> reported in the main output.</div><div><br></div><div> For delta_t < 0, the actual average rate of heating or cooling</div><div> should be roughly C*delta_t/(nraise*dt) (C=1 for an</div><div> ideal gas, C=0.5 for a harmonic solid, theorem of energy</div><div> equipartition between all quadratic degrees of freedom).</div></div><div><br></div><div>Why delta_t is a negative number is different from the document?</div></div></div><br><blockquote type="cite">
<br>Anyone has the same problem? And does anyone know how to heat the system up use the method "reduce-T"?<br></blockquote><div><br></div><div>I think "reduce-T" is used to quench the system, it reduces ionic temperature every "nraise" steps by the (negative) value "delta_t".</div><div><br></div><div>To heat the system up, I would suggest you to use other thermostats, like "rescaling", "rescale-v", "rescale-T", "berendsen" or "andersen".</div><div><br></div><div>Best wishes,</div><div>Changru</div><div><br></div><blockquote type="cite"><font class="Apple-style-span" color="#000000"><br></font>Thank you guys!<br><br>Rui
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<div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">---<br>Changru Ma<br>SISSA & Theory@Elettra group<br>email: <a href="mailto:crma@sissa.it">crma@sissa.it</a><br>tel: +39 040 378 7870<br><a href="http://www.sissa.it/~crma">http://www.sissa.it/~crma</a><br>---</div>
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