van der Waals Radii

Access van der Waals Radii information within QCElemental.

>>> qcel.vdwradii.get(6)
3.212534413278308
>>> qcel.vdwradii.get("C")
3.212534413278308
>>> qcel.vdwradii.get("C12")
3.212534413278308
>>> qcel.vdwradii.get("Carbon")
3.212534413278308

Contexts

To prepare for future changes, van der waals radii are contained in contexts. The qcel.vdwradii context will be updated over time to the latest data. To “pin” a context version, a specific context can be created like so:

>>> context = qcel.VanderWaalsRadii("MANTINA2009")
>>> qcel.vdwradii.get(6)
3.212534413278308

Currently only MANTINA2009 is available.

API

Top level user functions:

`get`(*[, return_tuple, units, missing])	Access a van der Waals radius for species `atom`.
`string_representation`()	Print name, value, and units of all van der Waals radii.

Function Definitions

qcelemental.vdwradii.get(atom, *, return_tuple=False, units='bohr', missing=None)

Access a van der Waals radius for species atom.

Parameters:

atom (Union[int, str]) – Identifier for element or nuclide, e.g., H, C, Al.
units (str) – Units of returned value. To return in native unit (MANTINA2009: angstrom), pass it explicitly. Only relevant for return_tuple=False since True returns underlying data structure with native units.
missing (Optional[float]) –
How to handle when atom is valid but outside the available data range. When None, raises DataUnavailableError. When a float, returns that float, so supply in units units. Supplying a float is a more compact assurance that a call will work over all the periodic table than the equivalent
```
try:
    rad = qcel.vdwradii.get(atom)
except qcel.DataUnavailableError:
    rad = 4.0
```
Only relevant for return_tuple=False.
return_tuple (bool) – See below.

Return type:

Union[float, Datum]

Returns:

float – When return_tuple=False, value of Van der Waals radius. If multiple defined for element, returns largest.
qcelemental.Datum – When return_tuple=True, Datum with units, description, uncertainty, and value of van der Waals radius as Decimal (preserving significant figures). If multiple defined for element, returns largest.

Raises:

NotAnElementError – If atom cannot be resolved into an element or nuclide or label.
DataUnavailableError – If atom is a valid element or nuclide but not one for which a van der Waals radius is available and missing=None.

qcelemental.vdwradii.string_representation()

Print name, value, and units of all van der Waals radii.

Return type:: str