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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 ($^{\wedge}$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 up previous contents
Next: The SCF calculation Up: Quick Start Previous: Creating the ``master input``

2000-04-11