Fast & Accurate Excited-State Calculations for PCBM: TDDFT vs sTDDFT
Part 6 of our AMS Weekly Video Series
This video shows how to model the absorption properties of the organic photovoltaic acceptor PCBM using Time-Dependent Density Functional Theory (TDDFT) and the more efficient simplified TDDFT (sTDDFT) in the Amsterdam Density Functional (ADF) program.
We begin by setting up a TDDFT calculation with the PBE functional and a TZP basis set to obtain excitation energies and oscillator strengths for the UV/Vis spectrum. While this approach provides a good balance between cost and accuracy, standard TDDFT can become computationally expensive for large molecules like PCBM, especially when many excited states are required.
To address this, the video demonstrates how sTDDFT offers a much faster alternative—allowing the use of hybrid functionals such as B3LYP with significantly reduced computational cost. A direct comparison shows that sTDDFT reproduces the experimental absorption peak near 340 nm more accurately while running several times faster than conventional TDDFT.
Using AMSSpectra, we visualize excitations, inspect orbital contributions, and analyze charge-transfer characteristics relevant to photovoltaic performance. The workflow provides a practical approach for studying excited-state trends in large organic semiconductors, with straightforward extensions to donor–acceptor complexes, substituent effects, and other device-relevant systems.
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