FCclasses3

FCclasses3 performs vibronic simulations of electronic spectra and nonradiative rates using harmonic and reduced-dimensionality models with curvilinear valence internal coordinates.

Key Features:

• Harmonic models: Implements vertical and adiabatic harmonic models describing initial and final states on quadratic potential energy surfaces (PES).
• Curvilinear coordinates: Uses curvilinear valence internal coordinates to expand PES at arbitrary molecular configurations.
• Reduced-dimensionality models: Constructs reduced-dimensionality models via projectors that isolate flexible coordinates from the harmonic subset.
• Anharmonic and mixed treatments: Enables isolated flexible coordinates to be treated with anharmonic or mixed quantum–classical approaches.
• Time-dependent methodologies: Implements time-dependent approaches for simulating dynamic and transient vibronic processes.
• Versatile spectroscopies: Supports one-photon absorption, two-photon absorption, emission, resonance Raman, and internal conversion rate simulations.

Scientific Applications:

• Electronic spectra and nonradiative rates (general): Simulation of vibronic contributions to electronic absorption, emission, and internal conversion rates across molecular systems.
• Rigid molecules — anthracene: Simulation of absorption and emission spectra for anthracene as an example of a rigid molecular system.
• Flexible molecules — polyphenyls: Simulation of spectra and vibronic effects in polyphenyl molecules exhibiting significant conformational flexibility.

Methodology:

Computations are based on the harmonic approximation with vertical and adiabatic harmonic models on quadratic PES, use of curvilinear valence internal coordinates and PES expansion at arbitrary configurations, construction of reduced-dimensionality models via projectors, optional anharmonic or mixed quantum–classical treatment of isolated coordinates, and time-dependent simulation methods.