[molpro-user] domains in local calculations

[Ben Shepler]

Dear Molpro Users,
I have been running local MP2 and CCSD(T) calculations on water  
clusters with various correlation consistent basis sets (aug-cc-pVnZ  
and cc-pVnZ with n=2,3,4).  I have been seeing what seems to be an  
unusual result in the selection of the orbital domains.

The orbital domains I would naively expect to get are as follows:   
for each water molecule 2 domains consisting of only basis functions  
from the O atom (lone pairs) and 2 domains each consisting of basis  
functions from the O atom and one of the Hs (OH bonds).  For almost  
all choices of basis set and using the same default value of  
THRBP=0.98 this is in fact what I am getting.  For example, here are  
the domains I get for the water trimer using the avqz basis and  
THRBP=0.98:

  Orbital domains

    Orb.   Atom     Charge      Crit.
    4.1    3 O7      1.12       0.000
           8 H8      0.60       1.000
    5.1    3 O7      1.10       0.000
           9 H9      0.56       0.999
    6.1    3 O7      1.34       0.997
    7.1    3 O7      1.26       0.999
    8.1    2 O4      1.26       0.999
    9.1    2 O4      1.34       0.997
   10.1    2 O4      1.12       0.000
           6 H5      0.59       1.000
   11.1    2 O4      1.10       0.000
           7 H6      0.55       0.999
   12.1    1 O1      1.10       0.000
           5 H3      0.56       0.999
   13.1    1 O1      1.34       0.997
   14.1    1 O1      1.26       0.999
   15.1    1 O1      1.12       0.000
           4 H2      0.60       1.000


I get the same domains for the vdz, vtz, vqz, avdz, and avqz basis  
sets.  The lone exception is the avtz basis where for the water  
trimer I get the domains:

  Orbital domains

    Orb.   Atom     Charge      Crit.
    4.1    3 O7      1.26       0.000
           8 H8      0.53       1.000
    5.1    3 O7      1.54       0.998
    6.1    3 O7      1.28       0.989
    7.1    3 O7      1.30       0.999
    8.1    2 O4      1.30       0.999
    9.1    2 O4      1.53       0.997
   10.1    2 O4      1.26       0.000
           6 H5      0.53       1.000
   11.1    2 O4      1.28       0.988
   12.1    1 O1      1.28       0.989
   13.1    1 O1      1.53       0.998
   14.1    1 O1      1.30       0.999
   15.1    1 O1      1.26       0.000
           4 H2      0.53       1.000

Further, if the avtz basis is used on the O atom and only vtz is used  
for the hydrogens I get the "expected" domains.  I can also get the  
"expected" domains with avtz by increasing THRBP to 0.99, or by using  
the option pipek,delete=2.

I see the same behavior in the water dimer, trimer, tetramer and  
hexamer.

I understand that it is important to increase THRBP as the basis set  
is increased, and that diffuse functions can cause problems in the  
localization procedure.  Therefore, on its own I am not surprised  
that the default options and the avtz basis do not give the  
"expected" domains.  It is a little surprising in light of the fact  
that the default options and the avqz basis set do.  I was also  
surprised to see the same behavior for the several different  
clusters.  Furthermore, when using the avtz basis the domains will  
change when looking at different configurations of the clusters.   
Again, this is perhaps not surprising on its own, but it has not been  
the case for any of the other basis sets I have tested.

Is it just a coincidence that the default options are not sufficient  
with the avtz basis here, or perhaps a coincidence that they are  
sufficient with the avqz basis in this case?  Is this a symptom that  
I am making some other mistake, or is it "normal" behavior when using  
the local methods?

Any insight anyone can share would be greatly appreciated.

regards,
Ben Shepler
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