<div dir="ltr"><div>ev.x enforces a lower (1) and an upper (15) bound on the derivative of the bulk modulus. I don't remember where they come from, but I am quite sure that dK0/dP ranges between 4 and 6 and never becomes negative or very large<br><br></div>Paolo<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jul 29, 2015 at 5:24 PM, anyy zsj <span dir="ltr"><<a href="mailto:zsjanyy@gmail.com" target="_blank">zsjanyy@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">similar but not the same. The fitting parameter for V0 is 1165.10028469 A^3, Bulk modulus is 808.33GPa and its derivative is -31.54200148. The derivative is very different.</div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jul 29, 2015 at 11:03 AM, Paolo Giannozzi <span dir="ltr"><<a href="mailto:p.giannozzi@gmail.com" target="_blank">p.giannozzi@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Which parameters do you obtain for V0 (equilibrium volume), K0 (bulk modulus), dK0/dP?<span><font color="#888888"><br><br></font></span></div><span><font color="#888888">Paolo<br></font></span></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jul 29, 2015 at 4:13 PM, anyy zsj <span dir="ltr"><<a href="mailto:zsjanyy@gmail.com" target="_blank">zsjanyy@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Thank you. But there is still a discrepancy for the following data set:<div><div>10.3 -54.420098694852939</div><div>10.4 -54.716135146323531</div><div>10.5 -54.894109787500000</div><div>10.7 -53.873787839705884</div></div><div>modified ev.x gives 10.46368, while the fitting is 10.52255.</div><div><br></div></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jul 29, 2015 at 4:23 AM, Paolo Giannozzi <span dir="ltr"><<a href="mailto:p.giannozzi@gmail.com" target="_blank">p.giannozzi@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div>Funny: one of the parameters of the fit is good for small unit cells, but too small for larger cells. In line 162 of PW/tools/ev.f90, replace<br> deltapar(1) = 0.1d0<br>with something larger:<br> deltapar(1) = 1.0d0<br></div>should be sufficient. Thank you for noticing this<span><font color="#888888"><br><br></font></span></div><span><font color="#888888">Paolo<br></font></span></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jul 28, 2015 at 6:06 PM, anyy zsj <span dir="ltr"><<a href="mailto:zsjanyy@gmail.com" target="_blank">zsjanyy@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">This data se<font face="arial, helvetica, sans-serif">t is actual calculated becaus</font>e I use a large supercell:<span><div><div style="font-size:14px">10.1 -48.570860572794118</div><div style="font-size:14px">10.3 -49.368013045588235</div><div style="font-size:14px">10.5 -49.714550792647060</div><div style="font-size:14px">10.7 -49.667482497058820</div><div style="font-size:14px">10.9 -49.305953287500003</div></div></span><div style="font-size:14px">But the fitting results are not compatible.</div></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">2015-07-28 12:01 GMT-04:00 Paolo Giannozzi <span dir="ltr"><<a href="mailto:p.giannozzi@gmail.com" target="_blank">p.giannozzi@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Please show me a set of data <b>produced by actual calculations</b> that ev.x doesn't fit properly<span><font color="#888888"><br><br></font></span></div><span><font color="#888888">paolo<br></font></span></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jul 28, 2015 at 5:51 PM, anyy zsj <span dir="ltr"><<a href="mailto:zsjanyy@gmail.com" target="_blank">zsjanyy@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Thank you very much!<div>Sure it is angstrom. My concern is that with the same data, ev.x and the manual fitting give different results as shown above. So I believe something is there.</div><div>The discrepancy is gone if I use a small lattice parameter. For example, if I scale the data by 1/3, both of them give the same results. So what's going on?</div></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">2015-07-28 11:44 GMT-04:00 Paolo Giannozzi <span dir="ltr"><<a href="mailto:p.giannozzi@gmail.com" target="_blank">p.giannozzi@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><span>On Tue, Jul 28, 2015 at 5:26 PM, anyy zsj <span dir="ltr"><<a href="mailto:zsjanyy@gmail.com" target="_blank">zsjanyy@gmail.com</a>></span> wrote:</span><div class="gmail_extra"><div class="gmail_quote"><span><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"> 1.4989396432 -6.0466776328<div><div> 1.5430233198 -6.0795705718</div><div> <a href="tel:1.5879629631" value="+15879629631" target="_blank">1.5879629631</a> -6.0993455319</div><div> 1.6804430727 -5.<a href="tel:9859764266" value="+19859764266" target="_blank">9859764266</a></div></div><div>The first column is volume and the second energy with Ry. After ev.x I input Ang, noncubic, 4, it gives me a results of 0.40 for minimal volume. It is certainly wrong.</div></div></blockquote><div><br></div></span><div>of course it is: ev.x assumes that the input data corresponds to a physical EOS. Your data isn't physical: the volume is way too small<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><br></div><div>Another example for the below data:</div><span><div><div>10.1 -48.570860572794118</div><div>10.3 -49.368013045588235</div><div>10.5 -49.714550792647060</div><div>10.7 -49.667482497058820</div><div>10.9 -49.305953287500003</div></div><div>The first column is lattice constant with angstrom and the second energy with Ry.</div></span></div></blockquote><span><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div> After ev.x I input Ang, sc, 4, it gives me 10.50369, while I get a different value 10.57517 by fitting to the formula in PRB 28,5480 (1983) of Murnaghan's equation.: <a href="http://gilgamesh.cheme.cmu.edu/doc/software/jacapo/appendices/appendix-eos.html" target="_blank">http://gilgamesh.cheme.cmu.edu/doc/software/jacapo/appendices/appendix-eos.html</a></div></div></blockquote></span><div><br> <div>sure that the first column is in angstrom and not a.u.? This is what I get assuming it is in a.u.:<br><br> # equation of state: murnaghan. chisq = 0.5402D-05<br># a0 = 10.5740 a.u., k0 =13776 kbar, dk0 = 4.17 d2k0 = 0.000 emin = -49.73649<br># a0 = 5.59554 Ang, k0 =1377.7 GPa, V0 = ******* (a.u.)^3, V0 =175.197 A^3 <br></div><br></div><div>note the small value of the |chi|^2 (chisq) of the fit<br><br></div><div>Paolo<br><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span><div dir="ltr"><div>I have tested many groups of data but the discrepancy is there for those large lattice parameters. Does ev.x use another equation or something else I have missing? Thank you very much.<br></div></div>
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