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Manuscript Title: Multi-electron systems in strong magnetic fields II: A fixed-phase diffusion quantum Monte Carlo application based on trial functions from a Hartree-Fock-Roothaan method
Authors: S. Boblest, D. Meyer, G. Wunner
Program title: Manteca
Catalogue identifier: AETV_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 185(2014)2992
Programming language: C++.
Computer: Cluster of 1-~ 500 HP Compaq dc5750.
Operating system: Linux.
Has the code been vectorised or parallelized?: Yes. Code includes MPI directives.
RAM: 500 MByte per node
Keywords: Neutron star magnetic fields, Atomic data, Quantum Monte Carlo.
PACS: 31.15.ac, 31.15.ve.
Classification: 2.1.

External routines: Boost::Serialization, Boost::MPI, LAPACK BLAS

Nature of problem:
Quantitative modellings of features observed in the X-ray spectra of isolated neutron stars are hampered by the lack of sufficiently large and accurate databases for atoms and ions up to the last fusion product iron, at high magnetic field strengths. The predominant amount of line data in the literature has been calculated with Hartree-Fock methods, which are intrinsically restricted in precision. Our code is intended to provide a powerful tool for calculating very accurate energy values from, and thereby improving the quality of, existing Hartree-Fock results.

Solution method:
The Fixed-phase quantum Monte Carlo method is used in combination with guiding functions obtained in Hartree-Fock calculations. The guiding functions are created from single-electron orbitals ψi which are either products of a wave function in the z-direction (the direction of the magnetic field) and an expansion of the wave function perpendicular to the direction of the magnetic field in terms of Landau states, ψi(ρ,φ,z) = Pi(zNLn=0tinΦni(ρ,φ), or a full two-dimensional expansion using separate z-wave functions for each Landau level, i.e. ψi(ρ,φ,z) = ΣNLn=0Pni(zni(ρ,φ). In the first form, the tin are expansion coefficients, and the expansion is cut off at some maximum Landau level quantum number NL. In the second form, the expansion coefficients are contained in the respective Pni.

Restrictions:
The method itself is very flexible and not restricted to a certain interval of magnetic field strengths. However, it is only variational for the lowest-lying state in each symmetry subspace and the accompanying Hartree-Fock method can only obtain guiding functions in the regime of strong magnetic fields.

Unusual features:
The program needs approximate wave functions computed with another method as input.

Running time:
1 minute - several days. The example provided takes approximately 50 minutes to run on 1 processor.