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Using Three-color Single-molecule FRET to Study the Correlation of Protein Interactions

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Sensitivity analysis of state-specific multireference perturbation theory.

Agnes Szabados¹

¹Laboratory of Theoretical Chemistry, Loránd Eötvös University, Budapest, Hungary. szabados@chem.elte.hu

The Journal of Chemical Physics

|May 10, 2011

Summary

State-specific multireference perturbation theory (SS-MRPT) can exhibit kinks on potential energy surfaces due to issues with model space coefficients. Sensitivity analysis reveals these problems are linked to root degeneracy in the effective Hamiltonian.

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Area of Science:

Quantum Chemistry
Computational Chemistry
Theoretical Chemistry

Background:

State-specific multireference perturbation theory (SS-MRPT) is a method for calculating electronic structure.
Potential energy surfaces calculated with SS-MRPT can exhibit unphysical features like kinks.
Related coupled-cluster methods may encounter convergence issues.

Purpose of the Study:

To investigate the origin of non-physical kinks in SS-MRPT potential energy surfaces.
To determine the role of model space coefficients in SS-MRPT inaccuracies.
To propose a method for identifying problematic coefficients.

Main Methods:

Analysis of the dependence of perturbed energy on initial model space coefficients.
Sensitivity analysis using singular values of sensitivity matrices.
Investigation of the influence of one-electron orbital nature on SS-MRPT behavior.

Main Results:

Non-physical kinks in SS-MRPT are not solely due to division by small coefficients.
Non-negligible model space coefficients can also be responsible for SS-MRPT problems.
A significant increase in coefficient sensitivities near problematic geometries indicates root degeneracy of the effective Hamiltonian.
Orbital rotations within the active space can exacerbate or mitigate these issues.

Conclusions:

Sensitivity analysis is a valuable tool for diagnosing SS-MRPT inaccuracies.
The degeneracy of the target root in the effective Hamiltonian is a key factor contributing to SS-MRPT problems.
Understanding the role of model space coefficients and orbital characteristics is crucial for reliable SS-MRPT calculations.