private BitSet getCellSet(int ix, int jy, int kz) {
		BitSet bs = new BitSet();
		Point3f cell = new Point3f(ix / 1000f, jy / 1000f, kz / 1000f);
		for (int i = atomCount; --i >= 0;)
			if (atoms[i].isInLatticeCell(cell))
				bs.set(i);
		return bs;
	}