Question

Is the morse potential cutoff (rc) we give is the local cutoff ? Is this potential require other cutoff a global cutoff?

I am using Morse potential to address the interactions between the pair of atoms. The cutoff usually I see in papers is very small (~5 angstrom).  The typical potential from used in simulations is
E = De.((1-exp(-a(r-r0)))**2 - 1.0)
The problem that I am facing is that when I am using a cutoff less than  r0 (equilibrium distance) I am getting the correct structure parameters and there is no issue. If I increase the cutoff more than r0 I am not getting correct results. If anyone used this Morse potential before please help me .

Top contributors to discussions in this field

27th Nov, 2016
Vasanth Kumar
University of Limerick
What you mean by structure parameters??RDF? Whats the system you are working on??how did you measure the structure parameters? Fix the cut-off to 12 Angstroms.
27th Nov, 2016
University College London
I am using GULP program to calculate the bulk modulus, elastic constants and equilibrium lattice constant. The material is SnTe it is a solid thermoelectric material. I am using different cutoff for different pair of atoms for example, 5 angs fro Sn-Sn interactions and 4 angs for Sn-Te interactions and so on. The Morse potential form is shown below
E = De.((1-exp(-a(r-r0)))**2 - 1.0)
We are fitting the potential parameters for this SnTe material using DFT data. During fitting I am getting r0 > rcut for Sn-Sn pair. This potential is able to reproduce the all above mentioned experimental values with <2% error. But my doubt is that is it correct using r0>rcut?
28th Nov, 2016
Vasumathi Velachi
University of Porto
May be possible.
Morse potential  is modelled to representing stretching and compression of covalent bonds connecting two atoms, So in your case, ro>rcut means then  the interaction between Sn-Sn might be compressed.

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