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Manuscript Title: Multi-electron systems in strong magnetic fields I: The 2D Landau-Hartree-Fock-Roothaan method
Authors: C. Schimeczek, G. Wunner
Program title: 2DLHFR
Catalogue identifier: AETE_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 185(2014)2655
Programming language: Fortran 95.
Computer: Cluster of 1-15 Fujitsu ESPRIMO P920.
Operating system: Linux.
Has the code been vectorised or parallelized?: Yes, parallelized using MPI. Tested on 2 to 60 processors.
RAM: At least 1 GByte per core
Keywords: Strong magnetic field, Atomic data, B-spline, Hartree-Fock-Roothaan.
PACS: 31.15.ag, 31.15.xr, 32.60.+i.
Classification: 2.1.

External routines: GFortran, LAPACK, BLAS, MPI

Nature of problem:
The modelling of highly magnetised atmospheres of neutron stars and magnetic white dwarfs is a difficult task and is further complicated by the lack of atomic data. The absorption features in the thermal emission spectra of neutron stars are still not fully understood, which leads to different interpretations and thus large uncertainties for the atmospheric parameters, such as the magnetic field strength, the gravitational redshift, or the predominant atomic composition. Therefore, a fast and reliable program to scan through the large parameter space is necessary.

Solution method:
The strong magnetic fields present on neutron stars favour a wave function expansion in terms of Landau channels. Contrary to previous attempts we use a full 2-dimensional basis and assign individual z-wave functions to each Landau channel. This allows for an accurate description of the single-particle orbitals. These are combined in a Slater determinant, resulting in Hartree-Fock-Roothaan equations, which are solved iteratively. As initial wave functions we rely on the solutions calculated by the HFFERII program and reuse the optimised B-spline basis sets and Landau coefficients to maximise the speed of the program presented here.

Intense magnetic field strengths B/Z2 >~ 5 × 104 T are required to yield accurate results.

Unusual features:
2DLHFR is based upon the wave functions calculated with the HFFERII program package, presented in [C. Schimeczek, D. Engel, G. Wunner, Comp. Phys. Comm. 183(2012)1502]. In turn, the results of this program may be enhanced beyond the Hartree-Fock limit with quantum Monte Carlo methods, as is shown in the accompanying paper.

Additional comments:
The gfortran compiler is recommemded for this program (http://gcc.gnu.org/onlinedocs/gfortran/).

Running time:
Seconds to minutes