  Radiation contributes to the acceleration of large-scale flows in various
astrophysical environments because of the strong opacity in spectral lines.
Quantification of the associated force is crucial to understanding these
line-driven flows, and a large number of lines (due to the full set of elements
and ionization stages) must be taken into account. Here we provide new
calculations of the dimensionless line strengths and associated
opacity-dependent force multipliers for an updated list of approximately 4.5
million spectral lines compiled from the NIST, CHIANTI, CMFGEN, and TOPbase
databases. To maintain generality of application to different environments, we
assume local thermodynamic equilibrium, illumination by a Planck function, and
the Sobolev approximation. We compute the line forces in a two-dimensional grid
of temperatures (i.e., values between 5,200 and 70,000 K) and densities
(varying over 11 orders of magnitude). Historically, the force multiplier
function has been described by a power-law function of optical depth. We
revisit this assumption by fitting alternative functions that include a
saturation to a constant value (Gayley's $\bar{Q}$ parameter) in the
optically-thin limit. This alternate form is a better fit than the power-law
form, and we use it to calculate example mass-loss rates for massive
main-sequence stars. Because the power-law force multiplier does not continue
to arbitrarily small optical depths, we find a sharp decrease, or quenching, of
line-driven winds for stars with effective temperatures less than about 15,000
K.
