code: @Override
      public DescriptorValue calculate(IAtom atom, IAtomContainer container) {
          if (factory == null)
              try {
                  factory = AtomTypeFactory.getInstance("org/openscience/cdk/config/data/jmol_atomtypes.txt",
                          container.getBuilder());
              } catch (Exception exception) {
                  return new DescriptorValue(getSpecification(), getParameterNames(), getParameters(), new DoubleResult(
                          Double.NaN), getDescriptorNames(), exception);
              }
  
          double covalentradius;
          try {
              String symbol = atom.getSymbol();
              IAtomType type = factory.getAtomType(symbol);
              covalentradius = type.getCovalentRadius();
              return new DescriptorValue(getSpecification(), getParameterNames(), getParameters(), new DoubleResult(
                      covalentradius), getDescriptorNames());
          } catch (Exception exception) {
              logger.debug(exception);
              return new DescriptorValue(getSpecification(), getParameterNames(), getParameters(), new DoubleResult(
                      Double.NaN), getDescriptorNames(), exception);
          }
      }
docs: This method calculates the Covalent radius of an atom.
  
  @param  atom              The IAtom for which the DescriptorValue is requested
  @param  container         The {@link IAtomContainer} for which the descriptor is to be calculated
  @return                   The Covalent radius of the atom