Examination of DFT and TDDFT methods II

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate prediction of molecular properties requires reliable computational methods.
• Understanding isomerization energies and excited states is crucial in chemical reactions and molecular behavior.
• Density Functional Theory (DFT) is a widely used method, but its performance varies with different functionals.

Purpose of the Study:

• To evaluate the performance of various DFT functionals in calculating isomerization energies for C8 alkanes and 1-X-propenes.
• To investigate the excited states of tropolone, focusing on proton transfer dynamics.
• To analyze the role of dispersion interactions and electron density in predicting these properties.

Main Methods:

• Time-Dependent Density Functional Theory (TDDFT) gradients were used to optimize adiabatic excited-state structures.
• Wave function files were generated for excited-state electron density analyses using 25 DFT functionals.
• Isomerization energies and excited-state properties were calculated and compared across different functionals.

Main Results:

• Dispersion interactions were found to be critical for accurate isomerization energy predictions for both alkanes and propenes.
• The B3LYP functional failed for C8 alkanes but succeeded for 1-X-propenes.
• Specific DFT functionals (M052X, BMK, CAM-B3LYP) showed superior performance in reproducing tropolone's excited-state proton transfer rates and barriers, with M052X uniquely capturing the faster rate in the excited state.

Conclusions:

• The choice of DFT functional significantly impacts the accuracy of calculated isomerization energies and excited-state properties.
• Correctly accounting for dispersion forces is essential for reliable isomerization energy predictions.
• Newly developed functionals demonstrate improved capabilities for complex excited-state dynamics, though underestimation of certain bond lengths remains a challenge.