5. XTP ASE Interface¶

5.1. Installation¶

5.1.1. Environment variables¶

The environment variable VOTCASHARE must be defined in order for the interface to find the default xml files and create the options data structure. You can set this environment variable in your shell configuration file:

$ export VOTCASHARE=/share/votca/

Or within python itself:

>>> os.environ['VOTCASHARE'] = '/share/votca/'

5.2. Option parser¶

The XTPOptions class is the preferred handler for setting all the options of the xtp calculator.

5.3. XTP calculator¶

Frequently used options can be specified using the calculator’s set routine.

keyword	type	default value	description
`label`	`str`	None	Name of input and output files
`xc`	`str`	None	XC functional to be used
`basisset`	`str`	None	Basis set to be used
`charge`	int	0	Charge of the molecule

5.4. Single Point Caclulation¶

Here is an example of setting up a calculation on a water molecule:

# Set up a water molecule
from ase.build import molecule
wat = molecule('H2O')

# Set up a XTP calculator
from pyxtp import xtp


# change options for the calculations
calc = xtp(label='water')
calc.options.dftpackage.functional = 'PBE'
calc.options.dftpackage.basisset = 'def2-svp'
calc.options.dftpackage.auxbasisset = 'aux-def2-svp'

# attach the calculator
wat.calc = calc

# compute the energy terms
wat.get_potential_energy()

5.5. Geometry Optimization¶

Here is an example of setting up a geometry of a carbon monoxide molecule using forces calculated on the first singlet state:

# Set up a water molecule
from ase.build import molecule
co = molecule('CO')
co.rattle()

# Set up a XTP calculator
from pyxtp import xtp

# change options for the calculations
calc = xtp()
calc.options.dftpackage.functional = 'PBE'
calc.options.dftpackage.basisset = 'def2-svp'
calc.options.dftpackage.auxbasisset = 'aux-def2-svp'

# specify the wich forces we want to use
calc.select_force(energy='singlets', level=0, dynamic=False)

# attach the calculator
co.calc = calc

# compute the energy terms
from ase.optimize import QuasiNewton
from ase.io import write
dyn = QuasiNewton(co, trajectory='test.traj')
dyn.run(fmax=0.01)
write('final.xyz', atoms)