Triplet carbonyls by MINDO/3

[RRS <RONSAUERS (- at -) rutchm.rutgers.edu>]

 Netters: We have just completed a fairly detailed series of computations
 of triplet state geometry and energy of formaldehyde and butanal by both
 ab initio (UMP2/6-311+G**) and UHF semi-empirical methods (AM1, PM1, MINDO/3,
 and MNDO).  We are struck by the finding that only MINDO/3 reproduces the
 non-planar structure (out-of-plane angles are ca. 40+ degrees) of the
 lowest triplet state of these molecules that one gets from ab initio
 methodology and from experimental determinations.
 	Can anyone explain why only MINDO/3 gives rise to the non-planar
 geometry and not the other semi-empirical methods?  I will post summaries
 of the answers.  Thanks, RRSauers