def GetDonor1FeatVects(conf, featAtoms, scale=1.5):
  """
  Get the direction vectors for Donor of type 1

  This is a donor with one heavy atom. It is not clear where we should we should be putting the
  direction vector for this. It should probably be a cone. In this case we will just use the
  direction vector from the donor atom to the heavy atom
    
  ARGUMENTS:
    
    featAtoms - list of atoms that are part of the feature
    scale - length of the direction vector
  """
  assert len(featAtoms) == 1
  aid = featAtoms[0]
  mol = conf.GetOwningMol()
  nbrs = mol.GetAtomWithIdx(aid).GetNeighbors()

  # find the neighboring heavy atom
  hnbr = -1
  for nbr in nbrs:
    if nbr.GetAtomicNum() != 1:
      hnbr = nbr.GetIdx()
      break

  cpt = conf.GetAtomPosition(aid)
  v1 = conf.GetAtomPosition(hnbr)
  v1 -= cpt
  v1.Normalize()
  v1 *= (-1.0 * scale)
  v1 += cpt
  return ((cpt, v1), ), 'cone'