The Los Alamos LEDCOP Opacity Code N.H. Magee, A.L. Merts, J.J. Keady and D.P. Kilcrease The Los Alamos Light Element Detailed Configuration OPacity code (LEDCOP) uses a basis set of detailed LS terms (plus average configuration terms for complex ion stages) to calculate opacities for elements with Z < 31. Each ion stage is considered in detail and interactions with the plasma are treated as pertubations. Calculations are done in local thermodynamic equilibrium (LTE) and only radiative processes are included. A self-consistent Hartree-Fock code[1,2] with relativistic corrections is used to generate both single configuration LS term energies, radial dipole matrix elements and angular factors for all ion stages and unresolved transition array (UTA) energies and variances in intermediate coupling for selected ion stages. This large quantity of atomic physics "data" is then reduced by fitting the term energies and dipole matrix elements with a quantum defect method and using the fits in the opacity code. Every energetically relevant configuration is included in the equation of state (EOS) and every allowed valence and inner shell transition from these configurations is used in the opacity calculations. Either the LS, UTA or statistical transition array model is chosen, depending on the complexity of the transition array and/or the plasma density. Nonhydrogenic photoionization cross sections are calculated for each configuration subshell with l < 5, using distorted wave continuum functions and the same Hartree-Fock structure calculations as for the bound-bound transtions in order to conserve oscillator strength across the photo- electric edges. Cross sections for n > 5, l > 4 are hydrogenic. The EOS model is based on the Saha equation, including degeneracy, where the bound Rydberg sequences are cut off by plasma corrections, including exchange and correlation. It does not consider liquid or solid phases, but uses an explicit ion model to treat, in detail, all of the bound electron states of every ionization stage. The modified Saha equation is solved iteratively to obtain a consistent set of ion abundances, bound state occupancies and free electrons. LEDCOP uses three different line profiles for bound-bound transitions. The general line shape is the Voigt convolution of a thermal Doppler (Gaussian) profile and a Lorentz profile with both natural and collision broadened halfwidths. Lyman and Balmer transitions from hydrogen-like ions and ground state transitions from helium-like ions use Stark profiles[14,15] based on APEX microfield calculations. A coherent scattering profile is used to modify resonance lines in the far line wings. The inverse bremsstrahlung is calculated from the Kramers cross section formula and relativistic free-free Gaunt factors. H- free-free and H- bound-free absorption are included for hydrogen. Free electron scattering is obtained from the Thomson cross section, modified by relativistic corrections and thermal motions, and collective effects. Opacities are calculated for pure elements on a standard temperature T, electron degeneracy "eta", and reduced photon energy (u=hv/kT) grid. The T-"eta" grid characterizes the plasma conditions at the ion sphere boundary for all elements. This allows the opacity of pure elements to be combined for mixtures without recalculating the basic data[20,21].  R.D. Cowan, The Theory of Atomic Structure and Spectra, University of California Press, Berkeley, (1981).  J. Abdallah, Jr., R.E.H. Clark, and R.D. Cowan, "CATS: Cowan Atomic Structure Code", LA-11436-M, Vol. 1, Los Alamos National Laboratory, (1988).  D.P. Kilcrease, J. Abdallah, Jr., J.J. Keady and R.E.H. Clark, J. Phys. B, vol. 26, L717 (1993).  R.E.H. Clark and A.L. Merts, JQSRT, vol. 38, 287 (1987).  P. Duffy, M. Klapisch, J. Bauche and C. Bauche-Arnoult, Phys. Rev. A, vol. 44, 5715 (1991).  R.E.H. Clark, GIPPER Photoionization Code, private communication.  W.J. Karzas and R. Latter, Ap. J. Suppl., vol. 6, 167 (1961).  A.N. Cox, "Stellar Absorption Coefficients and Opacities" eds. L.H. Allen and D.B. McLaughlin (Stars and Stellar Systems, Vol. 8, University of Chicago, Chicago, 1965), pg. 195.  J.C. Stewart and K.D. Pyatt, Ap. J., vol. 144, 1203 (1966).  F. Seitz, "The Modern Theory of Solids", (McGraw-Hill Book Company, New York, 1940), Mg. 365.  S.H. Vosko, L. Wilk, and M. Nusair, Can. J. Phys., vol. 58, 1200 (1980).  W.F. Huebner, "Atomic and Radiative Processes in the Solar Interior", ed. P.A. Sturrock (The Physics of the Sun, Vol. 1, D. Reidel Publishing Company, Dordrecht-Holland, 1986), pg. 33.  B.H. Armstrong, R.R. Johnson, H.E. DeWitt, and S.G. Brush, "Opacity of High Temperature Air" ed. C.A. Rouse (Progress in High of High Temperature Physics and Chemistry, Vol 1., Pergamon Press, Oxford, New York, 1966).  R.W. Lee, JQSRT, vol. 40, 561 (1988).  G.L. Olson, J.C. Comly, J.K. LaGattuta, and D.P. Kilcrease, JQSRT, vol. 51, 255 (1994).  M. Nakagawa, Y. Kohyama, and N. Itoh, Ap. J. Suppl., vol. 63, 661 (1987).  S. Geltman, Ap. J., vol. 141, 376 (1964).  S. Geltman, Ap. J., vol. 136, 935 (1962).  D.H. Sampson, Ap. J., vol. 129, 734 (1959).  W.F. Huebner, A.L. Merts, N.H. Magee, and M.F. Argo, "Astrophysical Opacity Library", LA-6760-M, Los Alamos National Laboratory, (1977).  J. Abdallah, Jr. and R.E.H. Clark, "TOPS: A Multigroup Opacity Code", LA-10454-M, Los Alamos National Laboratory, (1985).