<div dir="ltr"><div><div><div><div><div><div>I am new to QE. I have done variable cell volume optimization for rutile tio2.<br></div>I confused with finding ground state structure. <br><br></div>In literature survey the authors did volume- constraint total energy minimization and have set cell parameters a, c and internal parameter(  u for rutile)<br>
</div>finally fitted their value Birch - Murnaghan  equation(B-M) . From the final value they have compared their values with exprimental values of cell parameter <br>a,c and elastic parameters.<br><br></div>my question is:<br>
<br></div> i) which method is correct whether doing doing vc-relax alone  or collect all volume and total energy from vc-relax output and fitting this with B-M  equation ?<br><br></div> ii) How to choose internal parameter u for TiO2 rutile.?<br>
<div><div><div><div><div><div>i have included the input file. <br><br> &CONTROL<br>                       title = 'rutile' ,<br>                 calculation = 'vc-relax' ,<br>                restart_mode = 'from_scratch' ,<br>
                      outdir = '/home/basheer/Desktop/relax/' ,<br>                  pseudo_dir = '/home/basheer/espresso-5.0.1/pseudo/' ,<br>                      prefix = 'rutile' ,<br>               etot_conv_thr = 1.d-6 ,<br>
               forc_conv_thr = 1.d-4 ,<br>                     tstress = .true. ,<br>                     tprnfor = .true. ,<br> /<br> &SYSTEM<br>                       ibrav = 6,<br>                           A = 4.59373 ,<br>
                           B = 4.59373 ,<br>                           C = 2.95812 ,<br>                       cosAB = 0 ,<br>                       cosAC = 0 ,<br>                       cosBC = 0 ,<br>                         nat = 6,<br>
                        ntyp = 2,<br>                     ecutwfc = 200 ,<br>                     ecutrho = 800 ,<br>                 occupations = 'smearing' ,<br>                     degauss = 0.01 ,<br>                    smearing = 'gaussian' ,<br>
            exxdiv_treatment = 'gygi-baldereschi' ,<br> /<br> &ELECTRONS<br>                    conv_thr = 1.d-12 ,<br> /<br> &IONS<br> /<br> &CELL<br>               cell_dynamics = 'bfgs' ,<br>
              press_conv_thr = 2 ,<br> /<br>ATOMIC_SPECIES<br>   Ti   47.88800  Ti.pz-mt_fhi.UPF <br>    O   15.99900  O.pz-mt_fhi.UPF <br>ATOMIC_POSITIONS angstrom <br>   Ti      0.000000000    0.000000000    0.000000000    <br>
   Ti      2.296860000    2.296860000    1.479060000    <br>    O      1.402470000    1.402470000    0.000000000    <br>    O      3.191260000    3.191260000    0.000000000    <br>    O      0.894400000    3.699330000    1.479060000    <br>
    O      3.699330000    0.894400000    1.479060000    <br>K_POINTS automatic <br>  4 4 4   1 1 1 <br><br><br clear="all"></div><div><div><div><div><div dir="ltr"><div><div><div><div style="margin-left:40px;text-align:right">
                  <br></div><div style="text-align:right">A.Suresh,<br></div></div><div style="text-align:right">Project Fellow,<br></div></div><div style="text-align:right">Madurai Kamaraj University,<br></div></div><div style="text-align:right">
Madurai.<br></div></div></div>
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