Applications of quantum computing for investigations of electronic transitions in phenylsulfonyl-carbazole TADF emitters

A quantum chemistry study of the first singlet(S_(1))and triplet(T_(1))excited states of phenylsulfonyl-carbazole compounds,proposed as useful thermally activated delayed fluorescence(TADF)emitters for organic light emitting diode(OLED)applications,was performed with the quantum Equation-Of-Motion Variational Quantum Eigensolver(qEOM-VQE)and Variational Quantum Deflation(VQD)algorithms on quantum simulators and devices.These quantum simulations were performed with double zeta quality basis sets on an active space comprising the highest occupied and lowest unoccupied molecular orbitals(HOMO,LUMO)of the TADF molecules.The differences in energy separations between S_(1) and T_(1)(ΔEST)predicted by calculations on quantum simulators were found to be in excellent agreement with experimental data.Differences of 17 and 88 mHa with respect to exact energies were found for excited states by using the qEOM-VQE and VQD algorithms,respectively,to perform simulations on quantum devices without error mitigation.By utilizing state tomography to purify the quantum states and correct energy values,the large errors found for unmitigated results could be improved to differences of,at most,4 mHa with respect to exact values.Consequently,excellent agreement could be found between values ofΔEST predicted by quantum simulations and those found in experiments.

Excited state calculations using variational quantum eigensolver with spin-restricted ansätze and automatically-adjusted constraints

The ground and excited state calculations at key geometries, such as the Frank–Condon (FC) and the conical intersection (CI)geometries, are essential for understanding photophysical properties. To compute these geometries on noisy intermediate-scalequantum devices, we proposed a strategy that combined a chemistry-inspired spin-restricted ansatz and a new excited statecalculation method called the variational quantum eigensolver under automatically-adjusted constraints (VQE/AC). Unlike theconventional excited state calculation method, called the variational quantum deflation, the VQE/AC does not require the pre-determination of constraint weights and has the potential to describe smooth potential energy surfaces. To validate this strategy,we performed the excited state calculations at the FC and CI geometries of ethylene and phenol blue at the complete active spaceself-consistent field (CASSCF) level of theory, and found that the energy errors were at most 2 kcal mol−1 even on the ibm_kawasakidevice.