Could somebody please help me to understand.
In input file there is xred defining atoms positions.
But why there is only two positions in tutorial 3 for silicon crystal (code is below) ?
with only translational symmetries there is no way to construct crystal from only these two positions!
And in crystal structure databases like
http://rruff.geo.arizona.edu/AMS/amcsd.php or http://www.crystallography.net/
there is also not enough atoms!
what I do not know?
Code: Select all
# Crystalline silicon : computation of the total energy
#
#Definition of the unit cell
acell 3*10.18 # This is equivalent to 10.18 10.18 10.18
rprim 0.0 0.5 0.5 # In lessons 1 and 2, these primitive vectors
0.5 0.0 0.5 # (to be scaled by acell) were 1 0 0 0 1 0 0 0 1
0.5 0.5 0.0 # that is, the default.
#Definition of the atom types
ntypat 1 # There is only one type of atom
znucl 14 # The keyword "znucl" refers to the atomic number of the
# possible type(s) of atom. The pseudopotential(s)
# mentioned in the "files" file must correspond
# to the type(s) of atom. Here, the only type is Silicon.
#Definition of the atoms
natom 2 # There are two atoms
typat 1 1 # They both are of type 1, that is, Silicon.
xred # This keyword indicate that the location of the atoms
# will follow, one triplet of number for each atom
0.0 0.0 0.0 # Triplet giving the REDUCED coordinate of atom 1.
1/4 1/4 1/4 # Triplet giving the REDUCED coordinate of atom 2.
# Note the use of fractions (remember the limited
# interpreter capabilities of ABINIT)
