def SeparateAtomsByChemicalSymbol(lsAtoms,sTokenChemicalSymbol):
	"""Separate the list of atoms into two sets: with and without a certain chemical element symbol.
	[lsAtoms]: list, set of Crystal.crystal.Atom objects.
	[sTokenChemicalSymbol]: string, chemical element symbol for selected set of atoms.
	<retval>: tuple (list, selected atoms of token chemical element; list, other atoms).
	"""
	lsSelectedAtoms=[]
	lsOtherAtoms=[]
	for thisAtom in lsAtoms:
		if thisAtom.sChemicalSymbol==sTokenChemicalSymbol:
			lsSelectedAtoms.append(thisAtom)
		else:
			lsOtherAtoms.append(thisAtom)
	return lsSelectedAtoms,lsOtherAtoms