Abstract
Vibronic instabilities in periodic chains with arbitrary repeat units and with partially filled bands are investigated systematically. It is shown that in each case non-totally-symmetric distortions exist, coupled linearly to the degenerate electronic states at EF. Distortions of various geometries (LA, LO, TA, TO) can be involved and they may be twofold or fourfold degenerate themselves. Various symmetries can be broken and various types of kinks can appear; the translational period need not be enlarged.