mcscf:linear dependent AO basis

Just Got Here

4:33:38 PM PDT - Tue, May 8th 2012

Hi,
I am a fairly new user of NWChem and I seem to have run into trouble with linear dependence in my basis set.

I am running SCF calc followed by an MCSCF run using the 6-311+G* basis set.

The comment at the beginning of the SCF calculation is:

!! The overlap matrix has   3 vectors deemed linearly dependent with

   eigenvalues:

2.16D-06 2.48D-06 7.62D-06

whereupon it runs through the calculation, completes and MCSCF begins whereupon again it reads:

!! The overlap matrix has   3 vectors deemed linearly dependent with

   eigenvalues:

2.16D-06 2.48D-06 7.62D-06

mcscf:linear dependent AO basis        0

------------------------------------------------------------------------

------------------------------------------------------------------------

 current input line :  

   63: task mcscf energy      

------------------------------------------------------------------------

------------------------------------------------------------------------

There is an error in the specified basis set 

------------------------------------------------------------------------

and crashes. First, I am a little confused that the eigenvalues of the offending orbitals would remain identical between the beginning of the SCF and the beginning of the MCSCF if the MCSCF were reading out the results of the SCF run. To test this I directly specified the orbital outputs from the SCF and the input for the MCSCF but to no avail.

My next thought was to identify which atomic orbitals were responsible, however I cannot seem to id the appropriate keyword print out the orbitals in a readable fashion. If anyone has general suggestions regarding how to go about identifying the troublesome basis functions I would be very grateful.

Sincerely,
Adam

Forum Regular

5:14:18 PM PDT - Wed, May 9th 2012
Hi Adam, Can you post or send us your complete input file ? Thanks. -Niri Govind niri.govind@pnnl.gov

Forum Vet

5:39:56 PM PDT - Wed, May 9th 2012

Try running your calculations with the following set in the input file before any "task" command:

 set lindep:n_dep 0

What this does is effectively tell the code to not throw out any linear dependent function, which should let you run the MCSCF code.

Bert

[QUOTE=Adam May 8th 11:33 pm]Hi,

I am a fairly new user of NWChem and I seem to have run into trouble with linear dependence in my basis set.

I am running SCF calc followed by an MCSCF run using the 6-311+G* basis set.

The comment at the beginning of the SCF calculation is:

!! The overlap matrix has   3 vectors deemed linearly dependent with

   eigenvalues:

2.16D-06 2.48D-06 7.62D-06

whereupon it runs through the calculation, completes and MCSCF begins whereupon again it reads:

!! The overlap matrix has   3 vectors deemed linearly dependent with

   eigenvalues:

2.16D-06 2.48D-06 7.62D-06

mcscf:linear dependent AO basis        0

------------------------------------------------------------------------

------------------------------------------------------------------------

 current input line :  

   63: task mcscf energy      

------------------------------------------------------------------------

------------------------------------------------------------------------

There is an error in the specified basis set 

------------------------------------------------------------------------

Forum Regular

1:05:14 PM PDT - Mon, May 21st 2012

Some background

Hi Adam,

To detect linear dependencies in the AO basis NWChem will diagonalize the overlap matrix. Zero eigenvalues mean that the basis set is linear dependent. Hence small eigenvalues are an indication that you are close to linear dependent. Obviously as the basis set does not change between the SCF and the MCSCF calculation the linear dependency issue does not change either.

In the SCF package we work around this problem by transforming the AO basis to a basis of orthonormal vectors. We can at that stage eliminate the linear dependent components and optimize the SCF wavefunction only in the basis of the linearly independent orthonormal vectors. However it seems that the MCSCF module does not support this approach and always optimizes the wavefunction in the full basis.

There are a number of potential reasons as to why a basis set becomes linearly dependent:
1. The geometry is specified in the wrong units putting atoms unphysically close to eachother.
2. The use of Cartesian basis functions with higher angular momenta (d-functions and higher) which leads to the introduction of "contaminants" (i.e. the xx+yy+zz combination of d-functions actually results in an s-function)
3. Using really large basis sets.
Reason 2 can be addressed by switching your calculation to spherical harmonic basis functions. Reason 1 most likely does not apply here as you would see many more linear dependencies.

Obviously you can also try what Bert suggested and tell the code to ignore linear dependencies. This may cause problems though which express themselves in unphysical energies as the variational principle is no longer maintained. I have also had a quick look to see if there is a way to print the linearly dependent vectors. There are actually two ways to do this:

   print "initial vectors"

   print "initial vector analysis"

Whether this tells you anything useful I am not sure of. Whenever I have tried to tweak a basis set to remove linear dependencies it turned out I had to remove quite a few functions, to the point that it becomes worth asking if one should not use a different basis set.

I hope this helps,

    Huub

Forum >> NWChem's corner >> General Topics