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Initialization of the calculation (init_lapw)
After the two basic input files have been created, initalization of
the calculation is done by ``Run Programs Initialize
Calculation''. This runs the script init_lapw, which is
described in detail in section 5.1.2.
All actions of this script are logged in short in :log and in
detail in the file case.dayfile , which also
gives you a ``restart`` possibility when problems occurred.
Initializing the calculation will run several steps automatically,
where x is the script to start WIEN97 programs (see section:
5.1.1).
- x nn
- calculates the nearest neighbors up to a specified
distance and thus helps to determine the atomic sphere radii (you must
specify a distance factor f, e.g. 2, and all distances up to f * NN-dist.
are calculated)
- edit tic.outputnn
- check for overlapping spheres, coordination numbers and nearest
neighbor distances, (e.g. in the sodium chloride structure there
must 6 nearest and 12 next nearest neighbors). Using these distances
and coordinations you can check whether you put the proper positions
into your struct file or if you mad a mistake. nn also checks
whether your equivalent atoms are really crystallographically
equivalent and eventually writes a new struct-file which you may or
may not accept.
- You can now either edit tic.struct (usually you will set
RMT here) and re-run nn or continue with lstart.
Note: case.struct is a formatted file and you must keep
all numbers at the proper column!!! If you prefer to use the
at this point make sure that in the ``User
configuration'' (section 11.2.3, page
node192.html))
you have set ``Use Struct Generator''.
This can also be done by setting the environment variable
USEWIEN before starting WIEN in a BOX
- x lstart
- generates atomic densities (see section
6.2) and determines how the orbitals are treated in
the band structure calculations (i.e. as core or band states, with
or without local orbitals, ...). You are requested to specify
the desired exchange correlation potential and an energy
that separates valence from core states. For TiC select the
recommended potential option, 13 (GGA of Perdew-Burke-Ernzerhof
96) and an energy of -6.0 Ry.
- edit tic.outputst
- check the output (did you specify a proper atomic configuration,
did lstart converge, are the core electrons confined to the atomic
sphere?). Warnings for the radial mesh can usually be neglected
since it affects only the atomic total energy. lstart
generates tic.in0_st, in1_st, in2_st,
inc_st and inm. For Ti it selects automatically 1s,
2s, and 2p as core states, 3s and 3p will be treated with
local orbitals together with 3d, 4s and 4p valence states.
- Now you can either edit tic.inst (e.g. change the atomic
configuration) and re-run lstart, or continue.
- x symmetry
- generates from a raw case.struct file the
space group symmetry operations, determines the point group of the
individual atomic sites, generates the LM expansion for the lattice
harmonics (in case.in2_st) and local rotation matrices (in
case.struct_st).
- edit tic.outputs
- check the symmetry operations (they have been written to or
compared with already available ones in tic.struct by the
program symmetry) and the point group symmetry of the atoms (You may
compare them with the ``International Tables for X-Ray
Crystallography``). If the output does not match your expectations
from the ``Tables'', you might have made an error in specifying the
positions. The tic.struct file will be updated with
symmetry operations, positive or negativ atomic counter (for
``cubic'' point group symmetries) and the local rotation matrix.
- Now you can either edit tic.struct and re-run
symmetry, or continue.
- edit tic.in1_st
- As mentioned, the input files are generated automatically with
some default values which should be a reasonable choice for most
cases. Nevertheless we highly recommend that you go through these
inputs and become familiar with them. The most important parameter
here is RKMAX, which determines the number of basis functions (size
of the matrices). Values between 6-10 are usually reasonable.
- edit tic.in2_st
- Here you may limit the LM expansion (e.g. in cases without
symmetry you may truncate the LM series after L=4), change the value
of GMAX (in cases with small spheres (e.g. systems with H-atoms)
values up to 15-20 are recommended) or specify a different
BZ-integration method to determine the Fermi energy. For this
example you should use the default efmod-parameter of TETRA
(tetrahedron method). so that you can compare your results with the
test run.
- Now all generated inputs are copied (from case.in*_st
to case.in*). In cases without inversion symmetry the
files case.in1c, in2c are produced.
- x kgen
- generates a k-mesh in the Brillouin zone (BZ). You must
specify the number of k-points in the whole BZ (use 1000 for
comparison with the provided output, a ``good'' calculations needs
many more); choose short output (0). For details see section
6.4.
- edit tic.klist
- check the number of k-points in the irreducible wedge of the BZ
(IBZ) and the energy interval specified for the first k-point.
- You can now either rerun kgen (and generate a different
k-mesh) or continue. To find more unoccupied states at higher
energies, you might want to increase Emax in tic.klist, see
page node97.html.
Note: We recommend setting
the energy window in case.in1 rather than in case.klist.
Setting the range in case.klist is for backwards compatibility.
- x dstart
- generates a starting density for the SCF cycle by
superposition of atomic densities generated in LSTART. For details
see section 6.5.
- edit tic.outputd
- (check if gmax >gmin)
- Now you are asked, whether or not you want to run a
spin-polarized calculation (in such a case case dstart is
re-run to generate spin-densities). For TiC say no.
In case of troubles init_lapw can be killed (
C).
After you have fixed the problem (e.g. recompilation of a program
which requires larger dimension parameters) you can run it again and
init_lapw will restart with the last step of the previous run
(unless you explicitly specify that you want to start with a specific
program (e.g. lapw1) then you should add the option -s
PROGRAM).
Initialization of a
calculation (running init_lapw) will create all inputs for the
subsequent SCF calculation choosing some default options and values.
Next: The SCF calculation
Up: Quick Start
Previous: Creating the ``master input``
2000-04-11