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<p>Hi all,</p>
<p><br>
</p>
<p>I'm doing <span style="font-size: 12pt;">lattice constant optimization for monoclinic unit cell (ibrav) of CuO. During the calculation I found that the "a vector" doesn't seem to</span><span style="font-size: 12pt;"> be fixed like (a, 0, 0) along x-axis direction.
It rotates a little along y-axis. Here is one example of the CELL_PARAMETER in the output:</span></p>
<p><span style="font-size: 12pt;">---------------</span></p>
<p></p>
<div><span style="font-size: 12pt;">CELL_PARAMETERS (alat= 8.59525235)<br style="">
1.000026260 0.001522869 0.000000000<br style="">
-0.161678076 1.130837816 0.000000000<br style="">
0.000000000 0.000000000 0.836873694<br style="">
---------------</span></div>
<p></p>
<p><span style="font-size: 12pt;">Here you can see that a vector = (<span style="font-family: Calibri, Arial, Helvetica, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', NotoColorEmoji, 'Segoe UI Symbol', 'Android Emoji', EmojiSymbols; font-size: 16px; background-color: rgb(255, 255, 255);">1.000026260
0.001522869 0.000000000), not like (a, 0, 0). </span>I never had this problem in the past when I was doing vc-relax for other cubic (ibrav = 1), hexagonal (ibrav = 4) and rhombohedral (ibrav = 5) systems. I even tried to fix all the coordinates of the
Cu and O atoms to see how the lattice vectors would change. But it still made the a vector rotate to y-axis a little. Do you think it's because there is something wrong in my vc-relax input? I also pasted my input below for you to look at.</span></p>
<p><span style="font-size: 12pt;"><br>
</span></p>
<p><span style="font-size: 12pt;">Thank you,</span></p>
<p><span style="font-size: 12pt;">Xu Huang</span></p>
<p><span style="font-size: 12pt;">Department of Chemistry,</span></p>
<p><span style="font-size: 12pt;">University of Iowa</span></p>
<p><span style="font-size: 12pt;"><br>
</span></p>
<p><span style="font-size: 12pt;"></p>
<div>&CONTROL<br>
calculation = 'vc-relax',<br>
pseudo_dir = '/import/u/u1/uaf/uaxhuang1/pwf/',<br>
prefix = 'CuO',<br>
outdir = './temp/',<br>
etot_conv_thr = 1.0D-5,<br>
forc_conv_thr = 1.0D-4,<br>
! restart_mode = 'restart',<br>
/<br>
&system<br>
ibrav = 12,<br>
celldm(1) = 8.595680686,<br>
celldm(2) = 1.142694843,<br>
celldm(3) = 0.837058209,<br>
celldm(4) = -0.140538276,<br>
nat = 8, <br>
ntyp = 3,<br>
ecutwfc = 35,<br>
ecutrho = 280,<br>
occupations = 'smearing',<br>
smearing = 'mv',<br>
degauss = 0.02,<br>
nspin = 2,<br>
starting_magnetization(1) = 0.1,<br>
starting_magnetization(2) = -0.1,<br>
lda_plus_u = .true.,<br>
Hubbard_U(1) = 1.0d-10,<br>
Hubbard_U(2) = 1.0d-10,<br>
/<br>
&electrons<br>
electron_maxstep = 100,<br>
mixing_beta = 0.2,<br>
conv_thr = 1.0d-7,<br>
/<br>
&ions<br>
/<br>
&CELL<br>
press = 0.0,<br>
/<br>
ATOMIC_SPECIES<br>
Cu1 1.0 Cu.pbe-d-rrkjus.UPF<br>
Cu2 1.0 Cu.pbe-d-rrkjus.UPF<br>
O 1.0 O.pbe-rrkjus.UPF<br>
ATOMIC_POSITIONS (crystal)<br>
Cu2 0.250000000 0.000000000 0.250000000<br>
Cu1 0.750000000 0.500000000 0.250000000<br>
Cu1 0.750000000 0.000000000 0.750000000<br>
Cu2 0.250000000 0.500000000 0.750000000<br>
O 0.000000000 0.250000000 0.440456316<br>
O 0.500000000 0.250000000 0.940456316<br>
O 0.000000000 0.750000000 0.559543684<br>
O 0.500000000 0.750000000 0.059543684<br>
K_POINTS (automatic)<br>
6 6 6 1 1 1<br>
<br>
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