<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, Sans-Serif;font-size:14pt"><div><span>I am using QE 5.0.2 and I have a very basic question.</span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>To optimise the structure of a material, i started with known experimental lattice constants and calculated energy vs lattice to know the optimised lattice constants. </span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span><br></span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida
Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>Now i wish to apply the strain <br></span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>so i increased lattice constant 'a' by 2% (let us say)</span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span><br></span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>now i need to relax (i believe) to get optimised coordinates before proceeding further and wish to know force and stress as well.<br></span></div><div style="color:
rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><br><span></span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>So my question is i should consider it as 'relax' or "vc relax"</span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>if relax then following should work but unfortunately no<br></span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>tprnfor =
.TRUE.</span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>tstress = .TRUE.</span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>ion_dynamics = 'bfgs'<br></span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;">If i donot consider force and stress, then it gives me final coordinates</div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><br></div><div
style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;">Is the above step true in this particular set of problems of strain application or should i use variable cell.</div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;">i am little confused.<br><span></span></div><div style="color: rgb(0, 0, 0); font-size: 18.6667px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,Sans-Serif; background-color: transparent; font-style: normal;"><span>So<br></span></div><div> </div><div>--------------------------------------------------------------------- <br><br><b><font color="#0000ff" size="4">Sohail Ahmad</font></b></div><font color="#0000ff">King Khalid
University</font><div><font color="#0000ff">Abha, Saudi Arabia</font></div><div><font color="#0000ff"><br></font>--------------------------------------------------------------------<br></div></div></body></html>