VASP 2.0

Introduction

This module introduces an updated version of the ASE VASP calculator, which adds the functionality of the FileIOCalculator. This allows a more general usage of the other ASE methods, such as BandStructure.

For a general introduction please refer to the vasp calculator documentation, as this is just a list of things which have changed.

Warning

This calculator is currently in BETA testing. If you are not comfortable testing new software, please use the old calculator object, see vasp.

Note

If you encounter any bugs using this calculator, please report it as an issue on the ASE github or on the ASE IRC.

Environment variables

The calculator needs to know how to execute VASP. One way of doing this, is by using the command() method, with instructions on how to execute vasp, e.g.:

Vasp2(command='mpiexec vasp_std')

which requires that the executable vasp_std is in your PATH. Alternatively, similar to the original implementation, one of the following environment variables can be set: ASE_VASP_COMMAND, VASP_COMMAND or VASP_SCRIPT - note, that the environment variables are prioritized in that order, so if ASE_VASP_COMMAND is set, the two others are ignored. The variables ASE_VASP_COMMAND or VASP_COMMAND should be commands which executes vasp. Additionally, remember to set the VASP_PP_PATH. An example shell configuration could contain

$ export ASE_VASP_COMMAND="mpiexec vasp_std"
$ export VASP_PP_PATH=$HOME/vasp/mypps

Alternatively, the VASP_SCRIPT could be used, as described in the original VASP calculator documentation.

Vasp 2.0 Calculator

The VASP specific keywords are unchanged, and should be included as described in VASP calculator. See the official VASP manual for more details on the VASP specific keywords.

class ase.calculators.vasp.vasp2.Vasp2(atoms=None, restart=None, directory='', label='vasp', ignore_bad_restart_file=False, command=None, txt=None, **kwargs)[source]

ASE interface for the Vienna Ab initio Simulation Package (VASP), with the FileIOCalculator interface.

Parameters:

atoms: object
Attach an atoms object to the calculator.
label: str
Prefix for the output file, and sets the working directory. Default is ‘vasp’.
directory: str
Set the working directory. Is prepended to label.
restart: str or bool
Sets a label for the directory to load files from. if restart=True, the working directory from label is used.
txt: bool, None, str or writable object
  • If txt is None, default ouput stream will be to PREFIX.out, where PREFIX is determined by label, i.e. the default would be vasp.out.

  • If txt is False or ‘-‘ the output will be sent through stdout

  • If txt is a string a file will be opened, and the output will be sent to that file.

  • Finally, txt can also be a an output stream, which has a ‘write’ attribute.

  • Example:

    >>> Vasp2(label='mylabel', txt=None) # Redirect stdout to :file:`mylabel.out`
    >>> Vasp2(txt='myfile.txt') # Redirect stdout to :file:`myfile.txt`
    >>> Vasp2(txt='-') # Print vasp output to stdout
    
command: str
Custom instructions on how to execute VASP. Has priority over environment variables.

Note

Parameters can be changed after the calculator has been constructed by using the set() method:

>>> calc.set(prec='Accurate', ediff=1E-5)

This would set the precision to Accurate and the break condition for the electronic SC-loop to 1E-5 eV.

Examples

The Vasp FileIO calculator now integrates with existing ASE functions, such as BandStructure or bandgap.

Band structure with VASP

The VASP manual has an example of creating a Si band structure - we can easily reproduce a similar result, by using the ASE Vasp2 calculator.

We can use the directory keyword to control the folder in which the calculations take place, and keep a more structured folder structure. The following script does the initial calculations, in order to construct the band structure for silicon

from ase.build import bulk
from ase.calculators.vasp import Vasp2

si = bulk('Si')

mydir = 'bandstructure'    # Directory where we will do the calculations

# Make self-consistent ground state
calc = Vasp2(kpts=(4, 4, 4), directory=mydir)

si.set_calculator(calc)
si.get_potential_energy()  # Run the calculation

# Non-SC calculation along band path
kpts = {'path': 'WGX',     # The BS path
        'npoints': 30}     # Number of points along the path

calc.set(isym=0,           # Turn off kpoint symmetry reduction
         icharg=11,        # Non-SC calculation
         kpts=kpts)

# Run the calculation
si.get_potential_energy()

As this calculation might be longer, depending on your system, it may be more convenient to split the plotting into a separate file, as all of the VASP data is written to files. The plotting can then be achieved by using the restart keyword, in a second script

from ase.calculators.vasp import Vasp2

mydir = 'bandstructure'    # Directory where we did the calculations

# Load the calculator from the VASP output files
calc_load = Vasp2(restart=True, directory=mydir)

bs = calc_load.band_structure() # ASE Band structure object
bs.plot(emin=-13)               # Plot the band structure

Which results in the following image

../../_images/vasp_si_bandstructure.png

We could also find the band gap in the same calculation,

>>> from ase.dft.bandgap import bandgap
>>> bandgap(calc_load)
Gap: 0.474 eV
Transition (v -> c):
  (s=0, k=15, n=3, [0.000, 0.000, 0.000]) -> (s=0, k=27, n=4, [0.429, 0.000, 0.429])

Note

When using hybrids, due to the exact-exchange calculations, one needs to treat the k-point sampling more carefully, see VASP HSE band structure wiki.

Currently, we have no functions to easily handle this issue, but may be added in the future.

Density of States

Vasp2 also allows for quick access to the Density of States (DOS), through the ASE DOS module, see DOS. Quick access to this function, however, can be found by using the get_dos() function:

>>> energies, dos = calc.get_dos()