Xintian Feng

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A summary of the technical advances that are incorporated in the fourth major release of the Q-CHEM quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation(More)
Electronic structure aspects of singlet fission process are discussed. Correlated adiabatic wave functions of the bright singlet and dark multiexciton states of tetracene and pentacene dimers are analyzed in terms of their character (excitonic, charge-resonance, multiexciton). At short interfragment separation (3.5−4 Å), both multiexcitonic and singly(More)
A simple three-state model for the dynamics of the singlet fission (SF) process is developed. The model facilitates the analysis of the relative significance of different factors, such as electronic energies, couplings, and the entropic contributions. The entropic contributions to the rates are important; they drive the SF process in endoergic cases (such(More)
The effect of morphology on singlet fission (SF) efficiency was investigated by using a combination of high-level electronic structure methods and a simple three-state kinetic model. The calculations reproduce the observed differences in SF efficiency in different polymorphs of 1,3-diphenylisobenzofuran (DPBF) and 1,6-diphenyl-1,3,5-hexatriene (DPH), as(More)
The utility of the norms of one-particle density matrices, ∥γ∥, for understanding the trends in electronic properties is discussed. Using several model systems that are relevant in the context of singlet fission (butadiene, octatetraene, and ethylene dimer), the dependence of interstate properties (such as transition dipole moments and nonadiabatic(More)
We present a general implementation of the resolution-of-the-identity (RI) and Cholesky decomposition (CD) representations of electron repulsion integrals within the coupled-cluster with single and double substitutions (CCSD) and equation-of-motion (EOM) family of methods. The CCSD and EOM-CCSD equations are rewritten to eliminate the storage of the largest(More)
Singlet fission is a process in which a singlet exciton converts into two triplet excitons. To investigate this phenomenon, we synthesized two covalently linked 5-ethynyl-tetracene (ET) dimers with differing degrees of intertetracene overlap: BET-X, with large, cofacial overlap of tetracene π-orbitals, and BET-B, with twisted arrangement between tetracenes(More)
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