ABINIT, FHI-aims and other codes¶

ABINIT¶

A complete example is the ABINIT tutorial. The template directory holds the reference structure as POSCAR and one ABINIT input file (*.abi) that reads it with structure "poscar:POSCAR". The input sets everything else: pseudopotentials in the order of the POSCAR species, cutoff, k-point mesh and convergence.

ABINIT's POSCAR reader takes the element of each atom from the end of its coordinate line, so minelastic writes the strained POSCARs in that form; for the same reason two species of one element cannot be used. Magnetic sublattices are set with spinat, which minelastic also reads for the symmetry (Magnetic materials). collect reads the stress and forces from the newest *.abo file of each directory. With --relax-ions, ionmov 2, ntime 100 and tolmxf 1.0d-6 are appended unless the input sets ionmov. The cell must stay fixed (optcell 0), the ions must stay fixed for clamped-ion runs (no ionmov), and dataset-specific values of ionmov and optcell are not accepted.

FHI-aims¶

The template directory holds geometry.in (the reference structure) and control.in:

minelastic generate aims ref/ -o el          # geometry.in per strain state, control.in copied
# run aims in every directory, output in aims.out
minelastic collect el

control.in must request the stress (compute_analytical_stress .true.) and must not relax the cell (relax_unit_cell); otherwise generate stops with an error. For clamped ions it must not relax the atoms either. With --relax-ions, relax_geometry bfgs 1E-3 is added unless it is present. The FHI-aims reader is tested on an output distributed with ASE; minelastic has not been run with FHI-aims itself.

Any format ASE can write (CASTEP, SIESTA, ...)¶

The generic interface writes only the strained structure in each directory and copies further input files. The results are read back with ASE:

minelastic generate generic crystal.cell -o el --format castep-cell --filename crystal.cell \
    --extra crystal.param
# run the code in every directory
minelastic collect el --output crystal.castep --format castep-castep

The reference structure (crystal.cell here) is read with the same --format as the files that are written. Make sure the inputs request the stress and keep the cell fixed. Keep the ions fixed too, unless you want relaxed ions. minelastic info crystal.cell --format castep-cell shows the strain set first.

Anything else¶

The Python API separates the strain set from how the calculations are run, so stresses from any source can be used (Your own workflow).