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<div class="moz-cite-prefix">if nor celldm(1) [in Bohr] nor A [in
\AA] are given in input and the CELL_PARAMETERS card is given then
alat is defined as the length (in bohr) of the first vector in
CELL_PARAMETERS<br>
in your case 7.5*sqrt(2.0)=10.60660172 bohr<br>
<br>
if celldm(1) or A are given then the CELL_PARAMETERS are
interpreted as given in those units.<br>
In input atomic positions are given in the selected units, in
output they are always given in unit of the alat value
computed/defined in input.<br>
<br>
If you want to use AA as your input/output length unit the easiest
way is to define<br>
<br>
A=1.0 or celldm(1)=1.889726878 in the &system namelist<br>
CELL_PARAMETERS<br>
...<br>
ATOMIC_POSITIONS Angstrom [or alat since they are the same] <br>
...<br>
<br>
in output the positions and cell information will be given in
(input) alat units, that is in AA again.<br>
<br>
HTH<br>
<br>
stefano<br>
<br>
PS <br>
in your case the silicon cell contracted by<br>
0.487685488 * alat / 7.5 = 0.487685488 * sqrt(2) <br>
the final cell corresponds to an FCC with<br>
final_alat = input_alat * 0.487685488 / 0.5 = 10,345371472 bohr<br>
<br>
In these units the atomic coordinates are just <br>
0 0 0 and 1/4 1/4 1/4 (plus a small shift away from the origin due
to the fact that the center of mass remain fixed during
relaxation)<br>
<br>
<br>
<br>
On 21/12/2015 07:30, Ridwan Agbaoye wrote:<br>
</div>
<blockquote
cite="mid:1607877866.1260392.1450679433430.JavaMail.yahoo@mail.yahoo.com"
type="cite">
<div style="color:#000; background-color:#fff;
font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial,
Lucida Grande, sans-serif;font-size:16px">
<div
style="margin-top:1.2pt;margin-right:0in;margin-bottom:1.2pt;margin-left:0in"
id="yui_3_16_0_1_1450677059337_9717" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9719" class="">Good Morning
Everybody,<o:p id="yui_3_16_0_1_1450677059337_9721" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4526" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9724" class=""><o:p
id="yui_3_16_0_1_1450677059337_9726" class=""> </o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4557" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9729" class="">I need some
help with
the interpretation of vc-relax output and conversion from
alat to bohr<o:p id="yui_3_16_0_1_1450677059337_9731"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4557" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
class="" id="yui_3_16_0_1_1450677059337_10896">I want to do
vc-relax calculation for a monoclinic system but i decide to
start with silicon a face-centered cubic system to
understand the concept of vc-relax properly </span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4525" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9734" class="">I tried
vc-relax for
silicon and i got the following output <o:p
id="yui_3_16_0_1_1450677059337_9736" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4200" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9739" class="">Begin Final
Coordinate<o:p id="yui_3_16_0_1_1450677059337_9741" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9744" class="">New Unit Cell
volume =
276.90769au^3<o:p id="yui_3_16_0_1_1450677059337_9746"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9749" class="">CELL
PARAMETERS(alat=10.60660172)<o:p
id="yui_3_16_0_1_1450677059337_9751" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9754" class="">-0.487685488
-0.000000000 0.487685488<o:p
id="yui_3_16_0_1_1450677059337_9756" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9759" class=""> 0.000117363
0.487685488 0.487685488<o:p
id="yui_3_16_0_1_1450677059337_9761" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9764" class="">-0.487685488
0.487685488 -0.000000000<o:p
id="yui_3_16_0_1_1450677059337_9766" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9769" class="">ATOMIC
POSITIONS(alat)<o:p id="yui_3_16_0_1_1450677059337_9771"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9774" class="">si
-0.035697193 -0.035697193 -0.035697193<o:p
id="yui_3_16_0_1_1450677059337_9776" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9779" class="">si
0.208182292 0.208182292 0.208182292<o:p
id="yui_3_16_0_1_1450677059337_9781" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9784" class="">End
of Final coordinate<o:p id="yui_3_16_0_1_1450677059337_9786"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9789" class=""><o:p
id="yui_3_16_0_1_1450677059337_9791" class=""> </o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9794" class="">My
input file has <o:p id="yui_3_16_0_1_1450677059337_9796"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9799" class=""><o:p
id="yui_3_16_0_1_1450677059337_9801" class=""> </o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9804" class="">ibrav=0
nat=2 ntyp=2<o:p id="yui_3_16_0_1_1450677059337_9806"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9809" class=""><o:p
id="yui_3_16_0_1_1450677059337_9811" class=""> </o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9814" class="">CELL
PARAMETER cubic<o:p id="yui_3_16_0_1_1450677059337_9816"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9819" class="">-7.5000
0.0000 7.5000<o:p id="yui_3_16_0_1_1450677059337_9821"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9824" class="">0.0000
7.5000 7.5000<o:p id="yui_3_16_0_1_1450677059337_9826"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9829" class="">-7.5000
7.5000 0.0000<o:p id="yui_3_16_0_1_1450677059337_9831"
class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9834" class=""><o:p
id="yui_3_16_0_1_1450677059337_9836" class=""> </o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9839" class="">How exactly do
we derive our celldm(1) and how do we convert to bohr<o:p
id="yui_3_16_0_1_1450677059337_9841" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
class=""><br>
</span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
id="yui_3_16_0_1_1450677059337_9844" class="">Do we need to
convert the atomic position from alat to Bohr or Angstrom<o:p
id="yui_3_16_0_1_1450677059337_9846" class=""></o:p></span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class=""><span
style="font-size: 11pt; font-family: Helvetica, sans-serif;"
class=""><br>
</span></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class="" dir="ltr"><font
id="yui_3_16_0_1_1450677059337_11772" face="Helvetica,
sans-serif"><span style="font-size: 14.6666669845581px;"
id="yui_3_16_0_1_1450677059337_11773">must i use bohr as
the unit of CELL PARAMETERS or i can use Angstrom and
declare it as CELL PARAMETER(angstrom) </span></font></div>
<div style="margin: 1.2pt 0in;"
id="yui_3_16_0_1_1450677059337_4051" class="" dir="ltr"><font
face="Helvetica, sans-serif"><span style="font-size:
14.6666669845581px;"><br>
</span></font></div>
<div>
</div>
<div class="" dir="ltr" id="yui_3_16_0_1_1450677059337_9848"><br>
</div>
<div class="" dir="ltr" id="yui_3_16_0_1_1450677059337_9848"><o:p
class="" id="yui_3_16_0_1_1450677059337_11042">Agbaoye
Ridwan Olamide</o:p></div>
<div class="" dir="ltr" id="yui_3_16_0_1_1450677059337_9848"><o:p
class="" id="yui_3_16_0_1_1450677059337_11041">Federal
University of Agriculture, Abeokuta</o:p></div>
<div class="" dir="ltr" id="yui_3_16_0_1_1450677059337_9848"><o:p
class="">M.Sc.(in view)</o:p></div>
<div class="" dir="ltr" id="yui_3_16_0_1_1450677059337_9848"><o:p
class=""><a class="moz-txt-link-abbreviated" href="mailto:agbaoyeridwan@yahoo.com">agbaoyeridwan@yahoo.com</a></o:p></div>
</div>
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