The probability of athermal divacancy formation has been calculated analytically with the help of the hard sphere approximation for several f. c . c . and b. c . c. metals /l/. Obtained data agree well with the results of computer simulation of low energy cascades (E 5 1 keV). Here the ratio of divacancies t o isolated vacancies is about 1/2. However, for high energy cascades (E > 1 0 keV) the analytical calculations of the production probability give reduced values (by 3 to 4 times) compared to computer simulation.This discrepancy is caused b y the fact that the hard sphere approximation is not effective for a high energy projectile. Thus for the Born-Mayer potentialwhere r is the distance between atoms, A, a are constants being equal t o 22.5 keV and 2 . 0~1 0-l1 m, respectively, in the c a s e of copper /2/; the collision diameter b = a ln(ZA/E), is of the s a m e o r d e r of magnitude as the interatomic distance. If E = 1 0 keV, b is approximately by an o r d e r of magnitude less for high energies. The hard sphere approximation does not take into account such processes where a projectile is moving between two neighbouring atoms of a crystal lattice at distances of r > b and knocking out both of them by i t s own field. This collision t y p e is a many-body one in nature.The three-body collision takes place i f the impact parameters q1 and 9 2 between crystal lattice atoms 1 and 2 and a projectile are less than the dis-

In this contribution, we report on a study of the self-organization of extended linear polymer chains into condensed globules using molecular dynamics methods. We have found that condensed chains (globules) are amorphous or crystalline depending on the interaction potential between constituents. Any structure is formed in several stages. The structures obtained were used in further computer simulations to investigate such processes as compression, decompression, fracture, and flow. We have found that there are different types of fracture and plastic behavior with their own energy, fluctuation, and defect characteristics. On the basis of the computer simulation results obtained, the equation of motion is derived for the system of chain macromolecules slipping relative to each other. The equation takes into account the relaxation and friction in the system. The solution obtained gives the general law that connects stress, strain rate, molecular mass, potentinl relief, and temperature. It also gives sound physical grounds for some empirical relations that are used in polymer technology. sian). Khimia, Moscow (1978).

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on the occasion of his 80th birthdayThe method of molecular dynamics is used to compute binding energies of different configurations of vacancy clusters in nickel. The interatomic pair potential IS obtained according to the pseudopotential theory. It is found that in the range from divacancy to hexavacancy various atomic configurations are formed which can be considered as nuclei of dislocation loops, voids, and new crystal lattices.Die Methode der Molekulardynamik wird benutzt, um die Bindungsenergien verschiedener Konfigurationen von Leerstellenclustern in Nickel numerisch zu berechnen. Das interatomare Paarpotential wird entsprechend der Pseudopotentialtheorie erhalten. Es wird gefunden, daB im Bereich von der Doppelleerstelle bis zur Hexavakanz verschiedene atamare Konfigurationen gebildet werden, die als Keime fur Versetzungsschleifen, Hohlraume und neue Kristallgitter angesehen werden konnen.