Some Semiempirical Thoughts

   Some Semiempirical Thoughts
 1.  As Joe Leonard correctly suggested, I am not an employeee
 of Fujitsu.  Stewart Computational Chemistry is a private
 consulting concern.  Fujitsu is a customer.
 2.  I regret my observation on SAM-1.  However, let me explain.
 The results I reported for SAM-1 were taken from an official
 publication written by Prof Dewar, and approved for public
 release.
 3.  Drs Caoxian Jie and Jianguo Yu expressed interest over the
 Gaussians in AM1.  The history of these terms is as follows:
 In 1982 Prof Dewar asked me to work on correcting the known
 error in MNDO, specifically to correct for the excessive
 repulsions at roughly the van der Waals' distances.  After a
 short time, it became clear that the fault could be corrected
 using the method of operator equivalents: a modification to
 the core-core terms could mimic the true correction, which should
 more correctly have been made elsewhere.
 A Gaussian series is like a Fourier series: you can model any
 function you want with it.  For that reason, I chose to add
 Gaussians to the core-core terms.  This was intended as an
 interim measure; at least, that was my thought at that time.
 Hopefully, we can soon do away with operator equivalents,
 which really only treat the symptom and not the cause.
 4.  MOPAC-7 will be coming out in a few months.  Details are
 still not finalized, but should be in about a month.  At the
 present time, however, it looks likely that MOPAC-7 will
 have the following features:
  e.  Most important, the amount of high-quality code contributed
 by various people is at an alltime high.
  d.  Some symmetry has been added.
  b.  One, two, and three dimensional systems will be supported.
  c.  Electronic band-structures will be calculable.
  f.  In one form, MOPAC-7 will be placed in the public domain.
  g.  The Manual has been expanded.  This is in response to so
 many requests for more detail.
  a.  Copies of the program and the manual will be available from
      several sources, including QCPE.
 None of this is definite, of course.  For just now, MOPAC-7 should
 be regarded as `vaporware'.
 James J. P. Stewart
 Tel 719 488 9416
 FAX 719 488 9758
 E-mail jstewart.,at,.fai.com