12 research outputs found
Wavefunction Embedding for Molecular Polaritons
Polaritonic chemistry relies on the strong light-matter interaction phenomena
for altering the chemical reaction rates inside optical cavities. To explain
and to understand these processes, the development of reliable theoretical
models is essential. While computationally efficient quantum electrodynamics
self-consistent field (QED-SCF) methods, such as quantum electrodynamics
density functional theory (QEDFT) needs accurate functionals, quantum
electrodynamics coupled cluster (QED-CC) methods provide a systematic increase
in accuracy but at much greater cost. To overcome this computational
bottleneck, herein we introduce and develop the QED-CC-in-QED-SCF
projection-based embedding method that inherits all the favorable properties
from the two worlds, computational efficiency and accuracy. The performance of
the embedding method is assessed by studying some prototypical but relevant
reactions, such as methyl transfer reaction, proton transfer reaction, as well
as protonation reaction in a complex environment. The results obtained with the
new embedding method are in excellent agreement with more expensive QED-CC
results. The analysis performed on these reactions indicate that the strong
light-matter interaction is very local in nature and that only a small region
should be treated at the QED-CC level for capturing important effects due to
cavity. This work sets the stage for future developments of polaritonic quantum
chemistry methods and it will serve as a guideline for development of other
polaritonic embedding models
Variational quantum eigensolver boosted by adiabatic connection
In this work we integrate the variational quantum eigensolver (VQE) with the
adiabatic connection (AC) method for efficient simulations of chemical problems
on near-term quantum computers. Orbital optimized VQE methods are employed to
capture the strong correlation within an active space and classical AC
corrections recover the dynamical correlation effects comprising electrons
outside of the active space. On two challenging strongly correlated problems,
namely the dissociation of N and the electronic structure of the
tetramethyleneethane biradical, we show that the combined VQE-AC approach
enhances the performance of VQE dramatically. Moreover, since the AC
corrections do not bring any additional requirements on quantum resources or
measurements, they can literally boost the VQE algorithms. Our work paves the
way towards quantum simulations of real-life problems on near-term quantum
computers
Software for the frontiers of quantum chemistry:An overview of developments in the Q-Chem 5 package
This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design
Spin-Flip Unitary Coupled Cluster Method: Toward Accurate Description of Strong Electron Correlation on Quantum Computers
Quantum computers have emerged as a promising platform to simulate the strong
electron correlation that is crucial to catalysis and photochemistry. However,
owing to the choice of a trial wave function employed in the popular hybrid
quantum-classical variational quantum eigensolver (VQE) algorithm, the accurate
simulation is restricted to certain classes of correlated phenomena. Herein, we
combine the spin-flip (SF) formalism with the unitary coupled cluster with
singles and doubles (UCCSD) method via the quantum equation-of-motion (qEOM)
approach to allow for an efficient simulation of a large family of strongly
correlated problems. In particular, we show that the developed
qEOM-SF-UCCSD/VQE method outperforms its UCCSD/VQE counterpart for simulation
of the cis-trans isomerization of ethylene and the automerization of
cyclobutadiene. The predicted qEOM-SF-UCCSD/VQE barrier heights for these two
problems are in a good agreement with the experimentally determined values. The
methodological developments presented herein will further stimulate
investigation of this approach for the simulation of other types of
correlated/entangled phenomena on a quantum computer