Emma:
at first sight, your problem is due to inconsistency
in the lattice vectors and atomic coordinates.
You can define the vectors in hexagonal structure
in many ways, starting with
LatticeConstant 3.985 Ang
-------- and then ----------------------------------------
%block LatticeParameters
1.000 1.000 1.6723 90.000000 90.000000 120.000000
%endblock LatticeParameters
-------- as you do it, or (equivalently) -----------------
%block LatticeVectors
1.0 0.0 0.0
-0.5 0.86602540378 0.0
0.0 0.0 1.6723
%endblock LatticeVectors
-------- or as you tried ---------------------------------
%block LatticeVectors
0.500 -0.866025 0.000000
0.500 0.866025 0.000000
0.000 0.000000 1.672271
%endblock LatticeVectors
(which is not standard, but legal). However you note that in all cases
the angle between a_1 and a_2 is 120 degrees. Then the fractional
coordinates of your atoms #2,3, in order to get hexagonal layers, must be
(1/3 2/3 Z), (2/3, 1/3, -Z).
The way you define cordinates
AtomicCoordinatesFormat Fractional
%block AtomicCoordinatesAndAtomicSpecies
0.00000000 0.00000000 0.00000000 1
0.33333333 0.33333333 0.25000000 2
0.66666667 0.66666667 0.75000000 2
%endblock AtomicCoordinatesAndAtomicSpecies
would be OK if your lattice vectors be chosen with the angle 60 degrees.
(nonstandard but should work).
Andrei Postnikov
+-- Dr. Andrei Postnikov ---- Tel. +33-387315873 ----- mobile +33-666784053 ---+
| Paul Verlaine University - Institute de Physique Electronique et Chimie, |
| Laboratoire de Physique des Milieux Denses, 1 Bd Arago, F-57078 Metz, France |
+-- [EMAIL PROTECTED] ------------ http://www.home.uni-osnabrueck.de/apostnik/
--+
On Wed, 8 Nov 2006, Emma Sceats wrote:
| Dear SIESTA Users,
|
| I am trying to perform calculations on bulk CoI2 (cobalt diiodide) which has
| the Cd(OH)2/CdI2-type structure (P3-m1 space group).
|
| It is a hexagonal close pack (HCP) with the ABAB... structure. I have
| performed many calculations on fcc, bcc and cubic structures, but I cannot
| work out how to input the coordinates and lattice vectors for this HCP
| structure.
|
| I have tried several variations of coordinates and lattice vectors/parameters,
| including:
|
| ==========================================
| LatticeConstant 3.985 Ang # a=b=3.985Ang, c=6.664Ang. (c/a = 1.6723
| Ang) ref: S.R.Kuindersma,Physica (1981) 111, 231
|
| %block LatticeParameters
| 1.000 1.000 1.6723 90.000000 90.000000 120.000000
| %endblock LatticeParameters
|
| #%block LatticeVectors # taken from Navy
| website: http://cst-www.nrl.navy.mil/~mehl/phonons/hcp/
| # 0.500 -0.866025 0.000000 # 1/2, -1/2 3^1/3, 0
| # 0.500 0.866025 0.000000 # 1/2, 1/2 3^1/2, 0
| # 0.000 0.000000 1.672271 # 0, 0, c/a
| #%endblock LatticeVectors
|
| AtomicCoordinatesFormat Fractional
| AtomCoorFormatOut Ang
|
| %block AtomicCoordinatesAndAtomicSpecies
| 0.00000000 0.00000000 0.00000000 1
| 0.33333333 0.33333333 0.25000000 2
| 0.66666667 0.66666667 0.75000000 2
| %endblock AtomicCoordinatesAndAtomicSpecies
| ========================================
|
| Could someone perhaps explain to me what I am doing wrong and how/where to get
| appropriate coordinates and lattice vectors from?
|
| Thanks in advance
|
|
| Emma
|
|
|
