VQE Benchmarking of a Minimal π-Conjugated Molecule with Implications for DSSC-Oriented Quantum Simulations

Abstract

In the near term, quantum devices come with some strict limits on how big and complex the molecular systems can be when we use variational quantum algorithms. In this study, we apply the Variational Quantum Eigensolver (VQE) to ethylene (C2H4), which is a simple π-conjugated molecule. We chose it as a straightforward benchmark to validate quantum computational chemistry workflows while keeping in mind the realistic constraints of NISQ technology. Ethylene isn’t picked for its potential as a practical dye-sensitized solar cell (DSSC) sensitizer; rather, it serves as a clear π-conjugated bridge that maintains key features like electron delocalization, orbital symmetry, and correlation within a manageable active space. We compute the ground-state energy using a four-qubit active-space Hamiltonian, and we show clear variational convergence down to milli-Hartree precision. We also discuss frontier orbital analysis and electronic criteria related to DSSCs to provide a physical interpretation and to inspire future work on larger donor–π–acceptor structures when quantum hardware advances. This study sets up a controlled benchmark for evaluating the reliability, convergence behavior, and scalability of VQE-based molecular simulations in the realm of quantum materials modeling.