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Malathe,</div>
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I usually use vc-relax, so I dont know if it is the same in the relaxation calculation you are using, but the last step of vc-relax is a scf calculation with the relaxed structure. I just checked an old output file and you can check for this line in your relax
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<span>End of BFGS Geometry Optimization</span></div>
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<span> Final enthalpy = -395.6714252266 Ry</span></div>
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<span> A final scf calculation at the relaxed structure.</span></div>
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<div> The G-vectors are recalculated for the final unit cell</div>
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<div> Results may differ from those at the preceding step.</div>
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[...]</div>
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! total energy = -395.66904355 Ry</div>
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The energies are slightly different. If you are not satisfied with this energy you could of course perform a scf calculation on the relaxed structure and check that the energy is the same.</div>
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Good luck,</div>
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Brad</div>
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Bradly Baer</div>
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<span style="font-family:Calibri,Arial,Helvetica,sans-serif; background-color:rgb(255,255,255); display:inline!important">Graduate Research Assistant, Walker Lab</span><br>
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<span style="font-family:Calibri,Arial,Helvetica,sans-serif; background-color:rgb(255,255,255); display:inline!important">Interdisciplinary Materials Science</span><br>
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Vanderbilt University</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of Malathe Khalil <malathe.zero1@gmail.com><br>
<b>Sent:</b> Sunday, May 17, 2020 11:43 AM<br>
<b>To:</b> Quantum ESPRESSO users Forum <users@lists.quantum-espresso.org><br>
<b>Subject:</b> Re: [QE-users] (no subject)</font>
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<div>Dear Fabrizio </div>
<div dir="auto">I want to calculate the adsorption energy of a molecule on a surface. </div>
<div dir="auto">So I need the total energy of the clean slab. </div>
<div dir="auto">Can I just take the total energy from relax calculations output or I have to run scf ? </div>
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<div dir="auto">Thanks </div>
<div dir="auto">Malathe </div>
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<div dir="ltr" class="x_gmail_attr">On Sun, 17 May 2020, 6:04 pm Fabrizio Cossu, <<a href="mailto:fabrizio.cossu@apctp.org">fabrizio.cossu@apctp.org</a>> wrote:<br>
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<div dir="ltr" class="x_gmail_attr">On Sun, 17 May 2020 at 22:19, Malathe Khalil <<a href="mailto:malathe.zero1@gmail.com" target="_blank" rel="noreferrer">malathe.zero1@gmail.com</a>> wrote:<br>
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<div dir="auto">Dear QE users
<div dir="auto">What is the difference between the total energy generated by relax calculations and scf calculations? </div>
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<div>A structural relaxation is a scf calculation. Perhaps you mean a fixed point scf calculation, i.e. without updating the positions.<br>
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<div dir="auto">When I do relax calculations do I need to do scf calculations also?<br>
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<div>It depends on what you want to do. Do you want to compute some quantity self-consistently? AFAIK, some calculations require a different parameter set WRT the relaxation.<br>
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<div dir="auto">Thanks</div>
<div dir="auto">Malathe </div>
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