Subject: k-point for a one-d system

From: "nahoko matsuzawa" <[email-masked]>
Date: Fri, 13 Apr 2001 00:48:42 -0800

dear all,

I am now trying to use a planewave code to calculate
a polymer.  This should be a one dimension system.  I used
a tetragonal cell with about 15A in the x,y direction and
repeating the structure in the z direction.  Since it
is one D, I used  4 k-points on the (0 0 z) axis.  That
all went fine,  however when I accidentally did a calculation
using a Monkhorst-Pack generated k points set of 12 points
I got a total energy difference of 10 eV (with the value of 
the 12-points set being more negative).  

The 12-points-set is actually quite similar to the 4-points-set.
The z components are the same, but the (x,y) components are
now no longer (0,0) but substitute by three (x,y) combinations
for every z value of the 4-points-set. 

What is the case for this large difference in total energy?
Is the x-y direction of the unit cell not long enough?

Thank you very much in advance for your answer.

nahoko

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