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<p class="MsoNormal">Dear all,</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">I have a question regarding the “lefield” keyword in PW.x
code. I want to understand why if apply a positive electric field along the
x-direction (0.01 a. u.) of a monoclinic crystal, and then, subsequently a
negative electric field (-0.01 a. u.) along the same x-direction, the atomic forces
(in Ry/a.u.) change not only their sign but as well their magnitude (see below,
specially atoms 7 to 12 along the x-coordinate). In previous instances, I have
applied positive and negative electric fields along the x-direction of cubic
crystalline systems, and basically, I have obtained the same atomic forces but
with different signs. In my understanding, even, if I have a monoclinic crystal, changing the sign of an electric field should only change the sign of the atomic forces,
but not their magnitude; is this correct? </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Or what could be the reason for a change in both sign and
magnitude of the atomic forces, when one only changes the sign of the applied
electric field in monoclinic unit cells?</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Thanks for your help,</p>
<p class="MsoNormal">S. Sanchez</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Positive Electric Field<span style="">
</span>Forces acting on atoms (Ry/au):</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>1 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>0.01368508<span style=""> </span>-0.00000463<span style="">
</span>-0.01954027</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>2 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>0.01368346<span style=""> </span>-0.00000528<span style=""> </span>0.01953860</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>3 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>0.01377590<span style=""> </span>-0.00017516<span style="">
</span>-0.04026512</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>4 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>0.01377535<span style=""> </span>-0.00017479<span style=""> </span>0.04026785</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>5 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>0.01376076<span style=""> </span>0.00016477<span style=""> </span>0.04122506</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>6 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>0.01376443<span style=""> </span>0.00016449<span style="">
</span><span style=""> </span>-0.04122388</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>7 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>-0.05248836<span style=""> </span>0.00005249<span style=""> </span>0.00000005</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>8 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>0.00550320<span style=""> </span>-0.03398525<span style=""> </span>0.00000010</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>9 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>0.00562059<span style=""> </span>0.03391232<span style=""> </span>0.00000004</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>10 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>0.01308273<span style=""> </span>0.00010950<span style="">
</span>-0.00000080</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>11 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>-0.02716328<span style=""> </span>0.02288385<span style="">
</span>-0.00000081</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>12 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>-0.02699986<span style=""> </span>-0.02294231<span style="">
</span>-0.00000081</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Negative Electric Field<span style="">
</span>Forces acting on atoms (Ry/au): </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>1 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>-0.01378038<span style=""> </span>-0.00000119<span style="">
</span>-0.01953455</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>2 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>-0.01378055<span style=""> </span>-0.00000160<span style=""> </span>0.01953552</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>3 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>-0.01374417<span style=""> </span>0.00011193<span style="">
</span>-0.04120520</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>4 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>-0.01374465<span style=""> </span>0.00011173<span style=""> </span>0.04120524</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>5 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>-0.01375505<span style=""> </span>-0.00012449<span style=""> </span>0.04022320</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>6 type<span style="">
</span>2<span style=""> </span>force =<span style=""> </span>-0.01375511<span style=""> </span>-0.00012497<span style="">
</span>-0.04022321</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>7 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>-0.02545779 <span style=""> </span>-0.00007625<span style="">
</span>-0.00000018</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>8 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>0.03331831<span style=""> </span>-0.03352278<span style="">
</span>-0.00000019</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>9 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>0.03321440<span style=""> </span>0.03357830<span style="">
</span>-0.00000017</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>10 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>0.04024209<span style=""> </span>-0.00008227<span style="">
</span>-0.00000015</p>
<p class="MsoNormal"><span style=""> </span><span style=""> </span>atom<span style="">
</span>11 type<span style=""> </span>1<span style=""> </span>force =<span style="">
</span>0.00070042<span style=""> </span>0.02328288<span style=""> </span>-0.00000014</p>
<p class="MsoNormal"><span style=""> </span>atom<span style=""> </span>12 type<span style="">
</span>1<span style=""> </span>force =<span style=""> </span>0.00054247<span style=""> </span>-0.02315129<span style="">
</span>-0.00000018</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Here is the related Quantum Espresso input file:</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">&CONTROL</p>
<p class="MsoNormal"><span style=""> </span>calculation='scf'</p>
<p class="MsoNormal"><span style="">
</span>restart_mode='from_scratch',</p>
<p class="MsoNormal"><span style=""> </span><span style="" lang="PT-BR">prefix='na2o2',</span></p>
<p class="MsoNormal"><span style="" lang="PT-BR"><span style=""> </span>lelfield=.true.,</span></p>
<p class="MsoNormal"><span style="" lang="PT-BR"><span style=""> </span>nberrycyc=1</span></p>
<p class="MsoNormal"><span style="" lang="PT-BR"><span style=""> </span>pseudo_dir='$PSEUDO_DIR/',</span></p>
<p class="MsoNormal"><span style="" lang="PT-BR"><span style=""> </span></span>wf_collect=.true.,</p>
<p class="MsoNormal"><span style=""> </span>verbosity='high',</p>
<p class="MsoNormal"><span style=""> </span>tprnfor=.true.,</p>
<p class="MsoNormal"><span style=""> </span>outdir='./'</p>
<p class="MsoNormal">/</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">&SYSTEM</p>
<p class="MsoNormal">ibrav = 0,</p>
<p class="MsoNormal">a=1,</p>
<p class="MsoNormal">nat<span style=""> </span>=12,</p>
<p class="MsoNormal">ntyp =2, </p>
<p class="MsoNormal">ecutwfc = 80, </p>
<p class="MsoNormal">ecutrho = 320, </p>
<p class="MsoNormal">/ </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">&ELECTRONS</p>
<p class="MsoNormal"><span style="">
</span>diagonalization='david',</p>
<p class="MsoNormal"><span style=""> </span>conv_thr =<span style=""> </span>1.0d-8,</p>
<p class="MsoNormal"><span style=""> </span>mixing_beta = 0.5,</p>
<p class="MsoNormal"><span style="">
</span>startingwfc='random',</p>
<p class="MsoNormal">efield_cart(3)=0.0</p>
<p class="MsoNormal">efield_cart(2)=0.0</p>
<p class="MsoNormal">efield_cart(1)=0.01 -<span style="font-family: Wingdings;"><span style="">à</span></span> Change sign
accordingly between 0.01 or -0.01</p>
<p class="MsoNormal">/</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">CELL_PARAMETERS (alat)</p>
<p class="MsoNormal"><span style=""> </span>6.2199997902<span style=""> </span>0.0000000000<span style=""> </span>0.0000000000</p>
<p class="MsoNormal">-3.1099998951<span style="">
</span>5.3866778298<span style=""> </span>0.0000000000</p>
<p class="MsoNormal"><span style=""> </span>0.0000000000<span style=""> </span>0.0000000000<span style=""> </span>4.4699997902</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">ATOMIC_SPECIES</p>
<p class="MsoNormal">Na 23<span style="">
</span>Na.pz-n-vbc.UPF</p>
<p class="MsoNormal">O<span style=""> </span>16.0<span style=""> </span>O.pz-mt.UPF</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">ATOMIC_POSITIONS (crystal)</p>
<p class="MsoNormal"><span style="" lang="PT-BR">O<span style=""> </span><span style=""> </span>0.000000000<span style=""> </span>0.000000000<span style=""> </span>0.166999996<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">O<span style=""> </span>0.000000000<span style=""> </span>0.000000000<span style=""> </span>0.833000004<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">O<span style=""> </span>0.333333343<span style=""> </span>0.666666687<span style=""> </span>0.333000004<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">O<span style=""> </span>0.333333343<span style=""> </span>0.666666687<span style=""> </span>0.666999996<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">O<span style=""> </span>0.666666687<span style=""> </span><span style=""> </span>0.333333343<span style=""> </span>0.666999996<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">O<span style=""> </span>0.666666687<span style=""> </span>0.333333343<span style=""> </span>0.333000004<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">Na<span style=""> </span>0.723999977<span style=""> </span>0.000000000<span style=""> </span>0.500000000<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">Na<span style=""> </span>0.000000000<span style=""> </span>0.723999977<span style=""> </span>0.500000000<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">Na<span style=""> </span>0.276000023<span style=""> </span>0.276000023<span style=""> </span>0.500000000<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">Na<span style=""> </span>0.365999997<span style=""> </span>0.000000000<span style=""> </span>0.000000000<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">Na<span style=""> </span>0.000000000<span style=""> </span>0.365999997<span style=""> </span>0.000000000<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">Na<span style=""> </span>0.634000003<span style=""> </span>0.634000003<span style=""> </span>0.000000000<span style=""> </span></span></p>
<p class="MsoNormal"><span style="" lang="PT-BR"> </span></p>
<p class="MsoNormal"><span style="" lang="PT-BR">K_POINTS
{automatic}</span></p>
<p class="MsoNormal">2 2 2 0 0 0</p>
<p class="MsoNormal"> </p>