public double fy_i() {
		double d = 0.0;
		if (hasCharge_i && hasCharge_j)
			d += chargeChargeVsY_i();
		if (hasDipole_i && hasDipole_j)
			d += dipoleDipoleVsY_i();
		if (hasCharge_i && hasDipole_j)
			d += pjqiVsY_i();
		if (hasDipole_i && hasCharge_j)
			d += piqjVsY_i();
		return d * rCD;
	}