FAHViewer averageBondLength

double Atom::averageBondLength(const Atom &atom) const {
  // See: http://www.wiredchemist.com/chemistry/data/bond_energies_lengths.html
  const double table[][5] = {
    // H     C     N     O     S
    {0.74, 1.09, 1.01, 0.96, 1.34}, // H
    {1.09, 1.54, 1.47, 1.43, 1.82}, // C
    {1.01, 1.47, 1.45, 1.40, 1.43}, // N
    {0.96, 1.43, 1.40, 1.48, 1.43}, // O
    {1.34, 1.82, 1.43, 1.43, 1.49}, // S
  };

  int i = numberToIndex(number);
  int j = numberToIndex(atom.number);

  if (i == -1 || j == -1) return 2; // a wild guess

  return table[i][j];
}