Covalent Radii

Access Covalent Radii information within QCElemental.

>>> qcel.covalentradii.get(6)
>>> qcel.covalentradii.get("C")
>>> qcel.covalentradii.get("C12")
>>> qcel.covalentradii.get("Carbon")


To prepare for future changes, covalent radii are contained in contexts. The qcel.covalentradii 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.CovalentRadii("ALVAREZ2008")
>>> qcel.covalentradii.get(6)

Currently only ALVAREZ2008 is available.


Top level user functions:

get(*[, return_tuple, units, missing])

Access a covalent radius for species atom.


Print name, value, and units of all covalent radii.

Function Definitions

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

Access a covalent radius for species atom.

  • atom (Union[int, str]) – Identifier for element or nuclide, e.g., H, D, H2, He, hE4. In general, one value recommended for each element; however, certain other exact labels may be available. ALVAREZ2008: C_sp3, C_sp2, C_sp, Mn_lowspin, Mn_highspin, Fe_lowspin, Fe_highspin, Co_lowspin, Co_highspin

  • units (str) – Units of returned value. To return in native unit (ALVAREZ2008: 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

        rad = qcel.covalentradii.get(atom)
    except qcel.DataUnavailableError:
        rad = 4.0

    Only relevant for return_tuple=False.

  • return_tuple (bool) – See below.

Return type:

Union[float, Datum]


  • float – When return_tuple=False, value of covalent radius. If multiple defined for element, returns largest.

  • qcelemental.Datum – When return_tuple=True, Datum with units, description, uncertainty, and value of covalent radius as Decimal (preserving significant figures). If multiple defined for element, returns largest.

  • 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 covalent radius is available and missing=None.


Print name, value, and units of all covalent radii.

Return type: