private Point3f getCenterOfAtoms(int m, int n) {
		Point3f p = new Point3f();
		if (iAtom <= 0 || m >= n)
			return p;
		for (int i = m; i < n; i++) {
			p.x += atom[i].rx;
			p.y += atom[i].ry;
			p.z += atom[i].rz;
		}
		float inverse = 1.0f / (n - m);
		p.x *= inverse;
		p.y *= inverse;
		p.z *= inverse;
		return p;
	}