QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: ewilson on November 9, 2014, 02:57

Title: Extended Huckel Overlap Element Integration
Post by: ewilson on November 9, 2014, 02:57

Hi,

I'm curious what method (or methods) is used to perform the integration on the two-center integral of the Slater-Type Orbitals (STOs) in the Extended Huckel implementation.  STOs are a bit different to integrate, then say, Gaussians.  If there are multiple methods, is there a way to control this in ATK?

Thanks.

Title: Re: Extended Huckel Overlap Element Integration
Post by: ewilson on November 14, 2014, 19:40

Just wanted to give this a bump to prevent it from falling off the front page.

Title: Re: Extended Huckel Overlap Element Integration
Post by: Nordland on November 18, 2014, 22:57

The overlap matrix element is calculated using a combination of radial FFT and spherical bessel functions. There exist no alternative methods in ATK, because the correct implementation is 'exact' with the default parameters.

There are two parameters that you can set for this (reciprocal_energy_cutoff and number_of_reciprocal_points)
http://www.quantumwise.com/documents/manuals/ATK-13.8/ReferenceManual/ref.numericalaccuracyparameters.html
However I strongly recommend not playing with these parameters, as they will not make the calculation faster or more precise.
We are even consider removing them since playing with them could only lead to wrong calculations.