Browsing by Author "Evangelista, Francesco A."
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Item AGP-based unitary coupled cluster theory for quantum computers(IOP Publishing, 2022) Khamoshi, Armin; Chen, Guo P.; Evangelista, Francesco A.; Scuseria, Gustavo E.Electronic structure methods typically benefit from symmetry breaking and restoration, specially in the strong correlation regime. The same goes for ansätze on a quantum computer. We develop a unitary coupled cluster method based on the antisymmetrized geminal power (AGP)—a state formally equivalent to the number-projected Bardeen–Cooper–Schrieffer wavefunction. We demonstrate our method for the single-band Fermi–Hubbard Hamiltonian in one and two dimensions. We also explore post-selection as a state preparation step to obtain correlated AGP and prove that it scales no worse than O(√M) in the number of measurements, thereby making it a less expensive alternative to gauge integration to restore particle number symmetry.Item Direct triplet sensitization of oligothiophene by quantum dots(Royal Society of Chemistry, 2019) Xu, Zihao; Jin, Tao; Huang, Yiming; Mulla, Karimulla; Evangelista, Francesco A.; Egap, Eilaf; Lian, TianquanEffective sensitization of triplet states is essential to many applications, including triplet–triplet annihilation based photon upconversion schemes. This work demonstrates successful triplet sensitization of a CdSe quantum dot (QD)–bound oligothiophene carboxylic acid (T6). Transient absorption spectroscopy provides direct evidence of Dexter-type triplet energy transfer from the QD to the acceptor without populating the singlet excited state or charge transfer intermediates. Analysis of T6 concentration dependent triplet formation kinetics shows that the intrinsic triplet energy transfer rate in 1[thin space (1/6-em)]:[thin space (1/6-em)]1 QD–T6 complexes is 0.077 ns−1 and the apparent transfer rate and efficiency can be improved by increasing the acceptor binding strength. This work demonstrates a new class of triplet acceptor molecules for QD-based upconversion systems that are more stable and tunable than the extensively studied polyacenes.