*dk tmud2
      function tmud2 ( r )
c
c >>> tmud2 -- potential for (t-mu)+DD -- pair potential form
c
c --- on input the user supplies --
c
c     r -- array of length 3, giving the internuclear distances in
c              atomic units (bohrs)
c          r(1) = the BC distance (DD)
c          r(2) = the AC distance (tmu-D)
c          r(3) = the AB distance (tmu-D')
c
c --- on exit the function returns --
c
c     tmud2 -- value of the potential, in units specified by
c               the value of the variable "units" in common block
c               potpar.  if units=1., then atomic units are returned
c               for the potential (hartrees).  if units=27.2116, then
c               the potential is returned in electron volts.
c
c     note -- other parameters passed in the potpar common block are
c
c     vbase -- a reference potential, already in the desired output
c              units.  if vbase=0., then potntl = 0. when all three
c              distances get large.
c     emass -- mass of the "electron" for the h2(plus) potential.  if
c              the h2plus interaction is that of a d with a t-mu, then
c              emass should be 207 (approximately)
c
      implicit real*8 (a-h,o-z)
      dimension r(3)
      common / potpar / vbase, emass, units
c
      data ncall / 0 /
c
      ncall = ncall + 1
      if ( ncall .gt. 1 ) go to 10
      vbase = -14.874080d0
      emass = 232.51d0
      units = 1.0d0
   10 continue
c
      tmud2 = vh2(r(1)) + vh2p(r(2)) + vh2p(r(3)) - vbase
c
      return
      end