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Manuscript Title: The Madelung potential and electric field intensity for a sodium chloride and for a caesium chloride lattice.
Authors: U. Opik, R.F. Wood
Program title: NA CL MADELUNG FIELD
Catalogue identifier: ACMA_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 1(1970)281
Programming language: Fortran.
Computer: ICL 1907 1900 SERIES.
Operating system: QUBE.
RAM: 4K words
Word size: 24
Keywords: Solid state physics, Electrostatic Potential, Madelung, Nacl lattice, Cubic lattice, Point charge, Evjen, Crystal structure, Electrostatic field.
Classification: 7.8.

Nature of problem:
This version of subroutine MDLG calculates the electrostatic potential and the components of the electrostatic field at an arbitrary point in space within an infinite array of positive and negative point charges arranged in the form of a NaCl-type lattice.

Solution method:
The direct summation method due to Evjen.

Restrictions:
The subroutine will not deal with a distorted lattice. Not more than one of the point charges may have a value different from that appropri- ate to the perfect lattice.

Unusual features:
Provision has been made to avoid failure or loss of accuracy through division by zero or a very small number if the point at which the results are required is too close to one of the point charges.

Running time:
On the ICL 1907 machine, about 0.0024 (2l+1)**3 second for each call of the subroutine, where l(<=8) is the number stored in L (see long write- up and listing for the definition).