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Manuscript Title: Calculation of the nucleation and growth of defect clusters.
Authors: P.B. Kruger, R.M. Mayer
Program title: CLUSTER 78
Catalogue identifier: ACUE_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 18(1979)385
Programming language: Fortran.
Computer: IBM 370 MODEL 155.
Operating system: OSMVT.
RAM: 250K words
Word size: 8
Peripherals: disc, graph plotter.
Keywords: Solid state physics, Damage radiation, Defects point, Clusters, Nucleation, Growth, Dislocation loops, Voids, Chemical rate equations, Computation, Numerical integration.
Classification: 7.1.

Nature of problem:
The program calculates the probability of interaction of point defects, defect clusters and gas atoms using chemical rate reaction theory. The resulting set of differential equations is numerically integrated using a computer to give the number and size of the defect clusters as a function of irradiation time. The material is specified by listing certain constants and is applicable to elements and simple compounds.

Solution method:
The program is based on the subroutine of Gear, which integrates a set or ordinary differential equations by a step of length H. The trick is to keep H as large as possible so that the program can be run to times equivalent to displacing each atom in the lattice one hundred times. H is controlled by the subroutine wherever possible. In certain cases, however, H is set externally by extrapolation within the main program. Use of dimensionless quantities within the differential equations enables one to overcome rounding-off errors, which are typical of this type of calculation. Analytical solutions of the equations have not yet been found, apart from the one already published. The output of the program is in a form which can be directly compared with experiment, i.e. the number and average size of the clusters as a function of the irradiation time.

Running time:
To calculate the state of defect agglomeration to a dose equivalent to displacing each atom one hundred times takes typically between five and ten minutes.