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<p style="margin-top:0;margin-bottom:0">Hello </p>
<p style="margin-top:0;margin-bottom:0"><br>
</p>
<p style="margin-top:0;margin-bottom:0">I ran several DFTs few times before, but I only have limited amount of knowledge and experience in DFTs. </p>
<p style="margin-top:0;margin-bottom:0"><br>
</p>
<p style="margin-top:0;margin-bottom:0">I have Pyrope (Mg3Al2Si3O12) and Grossular (Ca<span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">3Al2Si3O12)
unit cell, and wish to preform relax and vc-relax. </span><span style="font-size: 12pt;">After I get the relaxed atomic structure and cell size, I wish to make an energy curve of Pyrope / Grossular structure w.r.t. compression and expansion of volume, </span><span style="font-size: 12pt;">using
expanded / compressed </span><span style="font-size: 12pt;">unit cells</span><span style="font-size: 12pt;">. </span><span style="font-size: 12pt;">Purpose of this DFT is to get the database for the parametrization of empirical force field, especially for
mechanical properties like stress-strain curve and elastic constants. </span></p>
<p style="margin-top:0;margin-bottom:0"><span style="font-size: 12pt;"></span></p>
<p style="margin-top:0;margin-bottom:0"><span style="font-size: 12pt;"><br>
</span></p>
<p style="margin-top:0;margin-bottom:0">Now, I have PBE-PAW(kjpaw) and PBESOL-PAW(kjpaw) PPs for all atom types. I have no problem about Pyrope, I can run it with PBESOL. But Grossular is an issue. <span style="font-size: 12pt;">F</span><span style="font-size: 12pt;">or </span><span style="font-size: 12pt;">Ca, </span><span style="font-size: 12pt;">PBE
is only available option from QE PP webpage, there is no PBESOL for Ca yet</span><span style="font-size: 12pt;">. Accordingly, if I want to calculate energies of Grossular structure, I have
</span><span style="font-size: 12pt;">three </span><span style="font-size: 12pt;">options as far as I know: </span></p>
<p style="margin-top:0;margin-bottom:0">1) input_dft = 'PBE', while mix the PBE (Ca) and PBESOL (Al, Si, O) </p>
<p style="margin-top:0;margin-bottom:0">2) inout_dft = 'PBESOL'<span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">,
while mix the PBE (Ca) and PBESOL (Al, Si, O)</span> </p>
<p style="margin-top:0;margin-bottom:0">3) just use PBE PPs for all 4 atom types. </p>
<p style="margin-top:0;margin-bottom:0"> </p>
<p style="margin-top:0;margin-bottom:0"><span style="font-size: 12pt;"></p>
<p style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">
At this point, I'm not sure what would be the good choice for my purpose. <span style="font-size: 12pt;">I wish to use PBESOL because it is known to have better prediction for solid properties. But I'm not sure if I can mix them with PBE, and if I mix, which
input_dft option should I need to choose. </span></p>
</span>
<p></p>
<p style="margin-top:0;margin-bottom:0"><span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;"><br>
</span></p>
<p style="margin-top:0;margin-bottom:0"><span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">I ran test relaxations for
3 cases, and </span><span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">I found that the </span><span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">final
atom coordinates of all 3 cases are very similar, they are mostly </span><span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">the
same up to </span><span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">second</span><span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;"> decimal
point numbers. Their final optimized </span><span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">energies are different,
but as far as I know I can't compare them, isn't it? I'm not sure on which criteria should I need compare and select the best one from those three </span>options.<br>
</p>
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</p>
<p style="margin-top:0;margin-bottom:0">Or, if anyone had a similar experience, I welcome any advises or suggestions. </p>
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</p>
<p style="margin-top:0;margin-bottom:0">Just in case, following is my example in file. </p>
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</p>
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<div>&CONTROL</div>
<div> prefix="03_Relax_Grossular_80_800_PBESOL",</div>
<div> calculation='relax',</div>
<div> outdir="/scratch/jj/20190501_QEDFT_Grossular_EoS/03_Relax_Grossular_80_800_PBESOL/tmp",</div>
<div> pseudo_dir="/home/QE_pseudo/",</div>
<div> restart_mode= 'from_scratch',</div>
<div> nstep = 1000</div>
<div>/</div>
<div><br>
</div>
<div>&SYSTEM</div>
<div> ibrav=0,</div>
<div> nat=20,</div>
<div> ntyp=4,</div>
<div> ecutwfc=80,</div>
<div> ecutrho=800,</div>
<div> occupations='smearing',</div>
<div> smearing='methfessel-paxton',</div>
<div> degauss=0.005000,</div>
<div> input_dft='PBESOL'</div>
<div>/</div>
<div><br>
</div>
<div>&ELECTRONS</div>
<div> diagonalization='cg',</div>
<div> conv_thr=1d-07,</div>
<div> mixing_mode='plain',</div>
<div> mixing_beta=0.100,</div>
<div>/</div>
<div><br>
</div>
<div>&IONS</div>
<div> ion_dynamics = 'bfgs',</div>
<div>/</div>
<div><br>
</div>
<div>ATOMIC_SPECIES</div>
<div> Ca 40.078000 Ca.pbe-spn-kjpaw_psl.1.0.0.UPF</div>
<div> Al 26.981539 Al.pbesol-n-kjpaw_psl.1.0.0.UPF</div>
<div> Si 28.085500 Si.pbesol-n-kjpaw_psl.1.0.0.UPF</div>
<div> O 15.999400 O.pbesol-n-kjpaw_psl.1.0.0.UPF</div>
<div><br>
</div>
<div>ATOMIC_POSITIONS {angstrom}</div>
<div>Ca 1.480750 0.000000 2.961500</div>
<div>Ca 2.961500 1.480750 0.000000</div>
<div>Ca 0.000000 2.961500 1.480750</div>
<div>Al 0.000000 0.000000 0.000000</div>
<div>Al 2.961500 2.961500 2.961500</div>
<div>Si 0.000000 2.961500 4.442250</div>
<div>Si 4.442250 0.000000 2.961500</div>
<div>Si 2.961500 4.442250 0.000000</div>
<div>O 0.450148 5.393484 1.791116</div>
<div>O 1.791116 0.450148 5.393484</div>
<div>O 5.393484 1.791116 0.450148</div>
<div>O 3.491016 2.511352 4.752616</div>
<div>O 2.511352 4.752616 3.491016</div>
<div>O 4.752616 3.491016 2.511352</div>
<div>O 5.472852 0.529516 4.131885</div>
<div>O 4.131885 5.472852 0.529516</div>
<div>O 0.529516 4.131885 5.472852</div>
<div>O 2.431984 3.411648 1.170385</div>
<div>O 3.411648 1.170385 2.431984</div>
<div>O 1.170385 2.431984 3.411648</div>
<div><br>
</div>
<div>K_POINTS {automatic}</div>
<div> 4 4 4 0 0 0</div>
<div><br>
</div>
<div>CELL_PARAMETERS {angstrom}</div>
<div> 5.923000000 0.000000000 0.000000000</div>
<div> 0.000000000 5.923000000 0.000000000</div>
<div> 0.000000000 0.000000000 5.923000000</div>
<br>
<p></p>
<p style="margin-top:0;margin-bottom:0">Thank you </p>
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</p>
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