**
Even-parity gap mode instability
**

The molecular dynamics simulations show that for the diatomic lattice,
an even-parity mode converts to an odd-parity mode but the converse is
not true. The speed of this transition depends on the relative
amplitude as shown in figure.
Time evolution of the even-parity anharmonic gap mode centered at site
300. Their amplitudes are:
(a) **A/d**=0.07;
(b) **A/d**=0.1;
and (c) **A/d**=0.13.
Each curve is
separated from the next by the time period of
32**T**_{m}, and shows the mean
kinetic energy averaged over
4**T**_{m}. The lowest curve identifies the
starting time. The lattice contains 601 particles so that any
reflected plane waves from the fixed boundary conditions do not
appear in this time interval.

Last modified: August 12, 1997