<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Dear S. Kumar,<div class=""><br class=""></div><div class="">maybe some developer will give you a more precise answer. However, just to make a remark, what I would say is that what one should also check</div><div class="">is to what extent a change in the conversion and/or in the alat would modify your results. </div><div class="">For example, as far as the the number</div><div class="">of decimal places is concerned, let us suppose that we are making a calculation of a cubic crystal with a = 3.40613 A and in place of it</div><div class="">we specify <font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">a = 3.4061 A. That would correspond to an underestimation of the lattice constant of less that 0.0009 %, much less than typical accuracy that</span></font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">can be reached by DFT in estimating the lattice constants. With such a small error, if you compute for example the band structure with</span></font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">the two values of the lattice parameter, you would appreciate no difference between the two (I would guess with changes in the eigenvalues</span></font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">much less that 1 meV).</span></font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class=""><br class=""></span></font></div><div class=""><font color="#000000" class="">Just to make an exercise, I tried with the following input, that concerns bulk silicon:</font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">&CONTROL<br class=""> calculation = 'scf'<br class=""> title = 'Silicon'<br class=""> restart_mode = 'from_scratch'<br class=""> outdir = './tmp/'<br class=""> prefix = 'Si'<br class=""> tprnfor = .true.<br class=""> pseudo_dir = './'<br class="">/<br class="">&SYSTEM<br class=""> ibrav = 2<br class=""> a = 5.43<br class=""> nat = 2<br class=""> ntyp = 1<br class=""> ecutwfc = 44<br class=""> ecutrho = 200<br class=""> nbnd = 8<br class="">/<br class=""> &ELECTRONS<br class="">/<br class="">ATOMIC_SPECIES<br class=""> Si 28.09 Si.pbe-n-kjpaw_psl.1.0.0.UPF<br class="">ATOMIC_POSITIONS { alat }<br class="">Si 0.00 0.00 0.00<br class="">Si 0.25 0.25 0.25<br class="">K_POINTS { automatic }<br class="">4 4 4 0 0 0</span></font></div><div class=""><font color="#000000" class=""><br class=""></font></div><div class=""><font color="#000000" class=""><br class=""></font></div><div class=""><font color="#000000" class="">With the shown value of a you get a total energy of -93.43935682 Ry and eigenvalues at Gamma point equal to</font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">-5.7252 6.2495 6.2495 6.2495 8.7945 8.7945 8.7945 9.6160</span></font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class=""><br class=""></span></font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">If I change a from 5.43 to 5.43005 (on the 5th digit, which corresponds to a change of 0.0009%) the previous quantities become</span></font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">-93.43935815</span> Ry and</font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">-5.7253 6.2492 6.2492 6.2492 8.7941 8.7942 8.7942 9.6154.</span></font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">The total energy changes by -0.00000133 Ry (-0.018 meV), the gap at Gamma point from 2.545 to 2.5449 (-0.1 meV).</span></font></div><div class=""><br class=""></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class=""><br class=""></span></font></div><div class=""><font color="#000000" class=""><span style="caret-color: rgb(0, 0, 0);" class="">Giovanni</span></font></div><div class=""><br class=""></div><div class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 23 Jan 2020, at 06:00, Sonu Kumar <<a href="mailto:1009ukumar@gmail.com" class="">1009ukumar@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="gmail_default" style="font-size:small">Dear QE developers,</div><div class="gmail_default" style="font-size:small"><br class=""></div><div class="gmail_default" style="font-size:small">I found that physical constant conversion factors are incorrect in the q-e version 6.2 and 6.4.1. For example, Bohr to ang conversion factor is around 0.5291772085900001, while nist codata value (<a href="https://physics.nist.gov/cgi-bin/cuu/Value?bohrrada0" class="">https://physics.nist.gov/cgi-bin/cuu/Value?bohrrada0</a>) is 5.291 772 109 03 e-11 m. This error is introduced in data-file-schema.xml files as lattice parameters are written in Bohr (provided input file contain lattice parameters in angstrom units). This error might lead to other erroneous physical quantities involving angstrom units. <br class=""></div><div class="gmail_default" style="font-size:small"><br class=""></div><div class="gmail_default" style="font-size:small">Also, output file contains 'lattice parameter (alat) =' values upto 4 decimal places; It will be better (in my opinion) to add more decimal places so as to check conversions to angstrom units or so.</div><div class="gmail_default" style="font-size:small"><br class=""></div><div class="gmail_default" style="font-size:small">Looking into the constants.f90 files in Modules in the src directory, I found the same. This is true for other constants mentioned in this file. <br class=""></div><div class="gmail_default" style="font-size:small"></div><div class="gmail_default" style="font-size:small"><br class=""></div><div class="gmail_default" style="font-size:small">With kind regards, sonu<br class=""></div><div class="gmail_default" style="font-size:small"><br class=""></div><div class="gmail_default" style="font-size:small"><br class=""></div><div class=""><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><span style="color:rgb(56,118,29)" class=""><b class=""><span style="background-color:rgb(243,243,243)" class=""></span></b></span><div class=""><span style="color:rgb(56,118,29)" class=""><b class=""><span style="background-color:rgb(243,243,243)" class="">With kind regards,<span class=""></span><br class=""></span></b></span></div><div class=""><span style="color:rgb(56,118,29)" class=""><b class=""><span style="background-color:rgb(243,243,243)" class="">S Kumar | PhD.<br class=""></span></b></span></div><div class=""><span style="color:rgb(56,118,29)" class=""><b class=""><span style="background-color:rgb(243,243,243)" class=""><span class="gmail_default" style="font-size:small">ICReDD</span><br class=""></span></b></span></div><span style="color:rgb(56,118,29)" class=""><b class=""><span style="background-color:rgb(243,243,243)" class=""></span></b></span></div></div></div></div></div></div></div></div></div></div></div></div>
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