Atom jumping atomic vibrational “attempt” frequency

The atoms in a crystal are vibrating continually with frequency v, which is usually taken to have a value of about 1013 Hz at room temperature. It is reasonable to suppose that the number of attempts at a jump, sometimes called the attempt frequency, will be equal to the frequency with which the atom is vibrating. The number of successful jumps that an atom will make per second, the jump frequency T, will be equal to the attempt frequency v, multiplied by the probability of a successful move, that is,... 

To be able to diffuse, an atom must surmount the energy barrier for migration presented by its neighbors. If vq is a characteristic atomic vibrational frequency, the probability for jump per second, v, is expressed as v = pq exp(—E /kT). The atom makes pq passes at the barrier with a probability exp(—Era/kT) on each try of surmounting it by thermal energy (pq is the so-called attempt frequency). 

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