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# FHI-aims

## Introduction

FHI-aims is a all-electron full-potential density functional theory code using a numeric local orbital basis set.

## Running the Calculator

The default initialization command for the FHI-aims calculator is

class ase.calculators.aims.Aims(profile=None, directory='.', **kwargs)

  Construct the FHI-aims calculator.

  The keyword arguments (kwargs) can be one of the ASE standard keywords: ‘xc’, ‘kpts’ and ‘smearing’ or any of FHI-aims’ native keywords.

  Arguments:

  cubes: AimsCube object

    Cube file specification.

  tier: int or array of ints

    Set basis set tier for all atomic species.

  plus_udict

    For DFT+U. Adds a +U term to one specific shell of the species.

  kwargsdict

    Any of the base class arguments.

In order to run a calculation, you have to ensure that at least the following `str` variables are specified, either in the initialization or as shell environment variables:

keyword | description
--- | ---
`run_command` | The full command required to run FHI-aims from a shell, including anything to do with an MPI wrapper script and the number of tasks, e.g.: `mpiexec aims.081213.scalapack.mpi.x > aims.out`. An alternative way to set this command is via the `ASE_AIMS_COMMAND` environment variable.
`species_dir` | Directory where the species are located, e.g.: `/opt/fhi-aims-081213/species_defaults/light`. Can also be specified with the `AIMS_SPECIES_DIR` environment variable.
`xc` | which exchange-correlation functional is used.

## List of keywords

This is a non-exclusive list of keywords for the `control.in` file that can be addresses from within ASE. The meaning for these keywords is exactly the same as in FHI-aims, please refer to its manual for help on their use.

One thing that should be mentioned is that keywords with more than one option have been implemented as tuples/lists, eg. `k_grid=(12,12,12)` or `relativistic=('atomic_zora','scalar')`. In those cases, specifying a single string containing all the options is also possible.

None of the keywords have any default within ASE, but do check the defaults set by FHI-aims.

Example keywords describing the computational method used:

keyword | type
--- | ---
`xc` | str
`charge` | float
`spin` | str
`relativistic` | list
`use_dipole_correction` | bool
`vdw_correction_hirshfeld` | str
`k_grid` | list

Note

Any argument can be changed after the initial construction of the calculator, simply by setting it with the method

    >>> calc.set(keyword=value)

## Volumetric Data Output

The class

class ase.calculators.aims.AimsCube(origin=(0, 0, 0), edges=[(0.1, 0.0, 0.0), (0.0, 0.1, 0.0), (0.0, 0.0, 0.1)], points=(50, 50, 50), plots=())

  Object to ensure the output of cube files, can be attached to Aims object

  parameters:

  origin, edges, points:

    Same as in the FHI-aims output

  plots:

    what to print, same names as in FHI-aims

describes an object that takes care of the volumetric output requests within FHI-aims. An object of this type can be attached to the main Aims() object as an option.

The possible arguments for AimsCube are:

keyword | type
--- | ---
`origin` | list
`edges` | 3x3-array
`points` | list
`plots` | list

The possible values for the entry of plots are discussed in detail in the FHI-aims manual, see below for an example.

## Example

Here is an example of how to obtain the geometry of a water molecule, assuming `ASE_AIMS_COMMAND` and `AIMS_SPECIES_DIR` are set: ase/test/calculator/aims/test_H2O_aims.py.

    # fmt: off
    import pytest

    from ase import Atoms
    from ase.calculators.aims import AimsCube
    from ase.optimize import QuasiNewton

    @pytest.mark.calculator('aims')
    def test_H2O_aims(factory):
        water = Atoms('HOH', [(1, 0, 0), (0, 0, 0), (0, 1, 0)])

        water_cube = AimsCube(points=(29, 29, 29),
                              plots=('total_density',
                                     'delta_density',
                                     'eigenstate 5',
                                     'eigenstate 6'))

        calc = factory.calc(
            xc='LDA',
            output=['dipole'],
            sc_accuracy_etot=1e-2,
            sc_accuracy_eev=1e-1,
            sc_accuracy_rho=1e-2,
            sc_accuracy_forces=1e-1,
            cubes=water_cube
        )

        water.calc = calc
        dynamics = QuasiNewton(water)
        dynamics.run(fmax=0.2)