allowable basis functions

allowable basis functions

Postby Graham Chandler » Tue Aug 30, 2016 8:02 pm

Dear NBO team,

I note an answer to Markus from Eric that says that NBO6 will give the error "Basis function not specified in expected form" if Cartesian f-functions are used instead of spherical f-functions. Three questions: Does this also hold for d-functions? Are the team considering incorporating use of Cartesian f and maybe d- functions? Does the same restriction to the requiring use of spherical functions apply to NBO 3. With NBO 3 no message about "Basis function not specified in expected form" appears, but I am getting some peculiar results using NBO 3 with Cartesian bases.

Kind regards,

Graham
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Re: allowable basis functions

Postby ericg » Mon Jul 03, 2017 10:24 pm

"Basis functions are not in expected form" doesn't have anything to do with Cartesian or spherical functions. NBO can handle both types of functions.

NBO6 evaluates overlap integrals using the basis function coefficients and exponents that it receives from the host program. If these integrals don't match the corresponding overlap matrix elements, NBO discards the basis functions and disables the analysis components that require these functions.

No such check is performed in NBO 3.1. I probably wouldn't trust the 3.1 results.

Eric

[Some additional information about basis functions: NBO6 demands that the AO basis functions be expressed in "standard form", in which the basis function coefficients pre-multiply unnormalized Gaussian primitives. NBO tests the basis functions of the host program to ensure that they are also in standard form. These tests are performed by comparing overlap integrals, explicitly calculated by NBO, to the overlap matrix elements provided by the host. Discrepancies likely suggest that the host program uses normalized Gaussian primitives. Discrepancies trigger NBO to normalize the primitive functions and to scale the basis function coefficients by the resulting normalization factors, thus converting the basis functions to NBO's standard form. If NBO is still unable, with the converted functions, to reproduce the overlap matrix elements, NBO reports "Basis functions are not in expected form" and discards the basis functions. Most likely, the host program isn't passing the basis function coefficients or exponents to NBO appropriately, if you receive this message.]
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