[CP2K-user] Binding Enery Curve for Si-S bond

Aniruddha Dive anirudd... at gmail.com
Wed Oct 17 18:34:37 UTC 2018

Hi All,

I want to generate a binding energy curve for a Si-S bond with bond lengths 
varying from 1.5 A - 7.5 A. To calculate the binding energy curve I have 
generated a SiH3-SH molecule where I vary the Si-S bond lengths from 1.5 A 
to 7.5 A over 25 different geometries. I run a geometry optimization for 
each geometry keeping the Si and S atoms fixed while allowing other atoms 
to relax. Based on the energies for all these geometries I obtain a binding 
energy curve for Si-S which flattens out giving a bond dissociation energy 
of 105 kcal/mol. The experimental Si-S bond dissociation energy reported is 
~ 145 kcal/mol which is significantly higher than what I obtain. To 
generate the binding energy curve I take all the energies to be relative to 
the minima which corresponds to zero energy.

I am thinking that this difference could be due to the BSSE effects when 
the Si-S atoms are at a larger separation leading to generation of two 
fragments SiH3 and SH. To determine the BSSE, I ran a BSSE calculations for 
the SiH3-SH molecule where the Si-S distance is 7.5 A. I obtain a 
CP-corrected total energy from these calculatons. Now, while generating the 
binding energy curve do I need to use the CP-corrected total energy as the 
total energy for that geometry? Or should I subtract this CP-corrected 
total energy from the total energy obtained during geometry optimization 
which will give me the BSSE. Further should I add the BSSE obtained to the 
relative energies for these geometries where the Si-S distance is larger 
than 3.0 A.

I have attached input file providing details about the GEO_OPT as well as 
BSSE and the coordinate file for one case.

Kindly let me know how can I generate an accurate binding energy curve for 
these molecules?

Aniruddha M Dive
PhD Candidate, Washington State University
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