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Dear Taiiebeh,<br>
<br>
K points are needed to describe the solid state effect (periodicity
...). In other words, you express the wave function of the system using
Bloch orbitals instead of molecular orbitals (in a cluster calculation).<br>
As a consequence, the dispersion in energy of the states contained in
the unit cell you have chosen is described using a periodic function in
which the wave vector k is defined. <br>
<br>
If the system you consider is 1D (i.e. 1D infinite chain along a), then
you need to define a k-mesh along the a* direction of the reciprocal
space. <br>
If 2D (lamellar system in (a, b) plane ): k-mesh along a* and b*.<br>
and if 3D: kmesh along all directions. <br>
<br>
In other words an isolated CNT is 1D along c, so you will need a k-mesh
like (1 1 X) with X defining the number of k-points along c* (where
your band structure will exhibit a dispersion of the energy levels
related to the sigma and pi states of the CNT).<br>
<br>
Concerning the number of k-points, you have to start with a small
number. Then increase progressively this number and compare the total
energies of each calculation. In such a way you will choose the
smallest mesh allowing to access a "converged" total energy (which does
not vary anymore by increasing the number of k points).<br>
<br>
Regards<br>
<br>
Xavier<br>
<br>
taiiebeh molarooy a écrit :
<blockquote cite="mid945109.20227.qm@web33605.mail.mud.yahoo.com"
type="cite">
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><font
face="arial"><span style="color: rgb(51, 51, 51); font-family: Arial;">Dear
wien users,</span><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;"></span></font></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="color: rgb(51, 51, 51); font-family: Arial;"><font face="arial">Hi,
</font></span><span
style="color: rgb(51, 51, 51); font-family: Arial;"><font face="arial">For
run scf of CNTs how should we select k-mesh? should we always select 1
k-mesh in b and c directions? why?</font></span></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="color: rgb(51, 51, 51); font-family: Arial;"><font face="arial">How
many k-points should be used? do number of k-point must be low? why?</font></span></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;"></span></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><font
face="arial"><span style="color: rgb(51, 51, 51); font-family: Arial;"></span><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;"></span></font></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><font
face="arial"><span style="color: rgb(51, 51, 51); font-family: Arial;"></span><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;"></span></font></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="color: rgb(51, 51, 51); font-family: Arial;"><font face="arial">Best
regards,</font></span></div>
<p> </p>
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