Benchmarking the Approximate Second-Order Coupled-Cluster Method on Biochromophores

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Biophysics

Background:

• Biochromophores in proteins like GFP, PYP, and rhodopsin are crucial for light absorption and signaling.
• Accurate computational methods are needed to understand their excited state properties.

Purpose of the Study:

• To benchmark approximate second-order coupled-cluster (CC2) and linear-response time-dependent density functional theory (TDDFT) for excited states of biochromophores.
• To assess the impact of basis sets and specific functionals (B3LYP) on accuracy.

Main Methods:

• Calculated excited state properties for 12 model chromophores from GFP, PYP, and rhodopsin.
• Employed CC2 and TDDFT (B3LYP) methods.
• Investigated basis set effects, including polarization and diffuse functions.

Main Results:

• Triple-ζ basis sets with polarization functions are sufficient for the lowest two excitation energies.
• Diffuse functions are needed for higher excited states and specific cases (anionic, Rydberg).
• CC2 results show excellent agreement (within 0.15 eV) with experimental data for GFP and rhodopsin chromophores.

Conclusions:

• CC2 offers high accuracy for excited state calculations of these biochromophores.
• TDDFT with B3LYP is less accurate but requires careful treatment of anions.
• Basis set choice significantly impacts accuracy for higher excited states.