SOFT MODES AND PROTON TUNNELING IN PbHPO4, SQUARIC ACID AND KH2PO4 TYPE FERROELECTRICS.

It is pointed out that the huge observed differences in the soft mode frequencies of KH//2PO//4, PbHPO//4, CsH//2PO//4 and squaric acid do not necessarily reflect a large difference in the proton O-H---O tunneling frequencies but rather result from a difference in the short range correlations renormalizing the single proton O--H-O tunneling frequency.