Optimizing internal coordinates

I'm trying to optimize an interaction between methyl sulfonate and a helium atom. I've input the cartesian coordinates of the sulfonate, a z-matrix for the helium, and used zcoor to (hopefully) keep the helium in the same orientation, so that it's only the interaction distance that I'm optimizing.

That said, it appears to run three mp3 calculations, each one giving the gradient along a different axis - is there any way of running it with internal coordinates? Just optimising along the He...O bond distance instead of along the helium position in x, y and z?

my input code is:

start h2o_freq

SCRATCH_DIR /mnt/beagle.tmp/jp.beagle/nwchemtemp/

memory total 3500 heap 500 stack 500 global 2500 mb

charge -1

geometry units angstroms

 zcoord

  angle 9 2 1 constant

  torsion 9 2 1 5 constant

  bond 9 2 constant

  angle 10 2 9 constant

  torsion 10 2 9 1 constant

 end

 zmatrix

  S1    -0.04945627     0.15646615    -0.00020389

  O1     1.33442349     0.69907524    -0.00102108

  O2    -0.81156737     0.41859072    -1.24926153

  O3    -0.81090550     0.42027917     1.24899274

  C1     0.18326515    -1.63017590     0.00016201

  H0    -0.79319973    -2.11765552     0.00142691

  H1     0.74047742    -1.91840156    -0.89316346

  H2     0.74136076    -1.91733246     0.89306828

  Bq1      O1     1.   S1  90.  C1    0.0

  He1     O1     2.1   Bq1  90.  S1 180.0

 zend

end



basis

 * library 3-21g*

end



set geometry:actlist 10

driver

 maxiter 100

end

title "N-acetyl taurine: 3-21g* RHF He interaction energy"

task scf optimize

basis

#basis is quite long so I've cut it out for the purposes of this post.

end

title "N-acetyl taurine : 6-311g(3d,3p) MP3 He interaction energy"

tce

 io replicated

 mp3

 print low

end

task tce optimize



scf; rhf; print low; end

mp2; print low; end[/quote]