[Pw_forum] K_POINTS, tpiba or crystal

Paul M. Grant w2agz at pacbell.net
Tue Dec 30 05:56:59 CET 2008

OK, let's get specific...suppose I want to generate a uniformly distributed
set of k-points for the reciprocal lattice of the primitive cell of an fcc
lattice.  The output of an scf run (and common sense matrix algebra) tells
me the reciprocal lattice is defined as

reciprocal axes: (cart. coord. in units 2 pi/a_0)
               b(1) = (  1.000000  0.000000  0.000000 )  
               b(2) = (  0.000000  1.000000  0.000000 )  
               b(3) = (  0.000000  0.000000  1.000000 )  

OK (again)...I now generate a(n) uniformly distributed grid over the "b"
vectors, and plot the points via xcrysden with PRIMVEC as above and see that
grid fills the entire basic reciprocal cell (that is, with translation
vector = O).  No specification of celldm(1).

Now, I want to input this grid to an nscf run via K_POINTS...is my grid
"tpiba" or "crystal?"

BTW, we (this community) owe a huge debt to Paolo and Axel.

Paul M. Grant, PhD
Principal, W2AGZ Technologies
Visiting Scholar, Applied Physics, Stanford (2005-2008)
EPRI Science Fellow (Retired)
IBM Research Staff Member Emeritus
w2agz at pacbell.net

-----Original Message-----
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
Behalf Of giannozz at democritos.it
Sent: Monday, December 29, 2008 12:29 PM
To: pw_forum at pwscf.org
Subject: Re: [Pw_forum] K_POINTS, tpiba or crystal

Quoting "Paul M. Grant" <w2agz at pacbell.net>:

> Frankly, I don't understand what "crystal" means wrt to reciprocal space

it means "in units of the reciprocal lattice primitive vectors"


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