6 research outputs found
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What Levels of Coupled Cluster Theory Are Appropriate for Transition Metal Systems? A Study Using Near-Exact Quantum Chemical Values for 3d Transition Metal Binary Compounds.
Transition metal compounds are traditionally considered to be challenging for standard quantum chemistry approximations like coupled cluster (CC) theory, which are usually employed to validate lower level methods like density functional theory (DFT). To explore this issue, we present a database of bond dissociation energies (BDEs) for 74 spin states of 69 diatomic species containing a 3d transition metal atom and a main group element, in the moderately sized def2-SVP basis. The presented BDEs appear to have an (estimated) 3Ï error less than 1 kJ/mol relative to the exact solutions to the nonrelativistic Born-Oppenheimer Hamiltonian. These benchmark values were used to assess the performance of a wide range of standard single reference CC models, as the results should be beneficial for understanding the limitations of these models for transition metal systems. We find that interactions between metals and monovalent ligands like hydride and fluoride are well described by CCSDT. Similarly, CCSDTQ appears to be adequate for bonds between metals and nominally divalent ligands like oxide and sulfide. However, interactions with polyvalent ligands like nitride and carbide are more challenging, with even CCSDTQ(P)Î yielding errors on the scale of a few kJ/mol. We also find that many perturbative and iterative approximations to higher order terms either yield disappointing results or actually worsen the performance relative to the baseline low level CC method, indicating that complexity does not always guarantee accuracy
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Computing Free Energies with Fluctuation Relations on Quantum Computers
Fluctuation relations allow for the computation of equilibrium properties,
like free energy, from an ensemble of non-equilibrium dynamics simulations.
Computing them for quantum systems, however, can be difficult, as performing
dynamic simulations of such systems is exponentially hard on classical
computers. Quantum computers can alleviate this hurdle, as they can efficiently
simulate quantum systems. Here, we present an algorithm utilizing a fluctuation
relation known as the Jarzynski equality to approximate free energy differences
of quantum systems on a quantum computer. We discuss under which conditions our
approximation becomes exact, and under which conditions it serves as a strict
upper bound. Furthermore, we successfully demonstrate a proof-of-concept of our
algorithm using the transverse field Ising model on a real quantum processor.
The free energy is a central thermodynamic property that allows one to compute
virtually any equilibrium property of a physical system. Thus, as quantum
hardware continues to improve, our algorithm may serve as a valuable tool in a
wide range of applications including the construction of phase diagrams,
prediction of transport properties and reaction constants, and computer-aided
drug design in the future
Computing Free Energies with Fluctuation Relations on Quantum Computers
One of the most promising applications for quantum computers is the dynamic
simulation of quantum materials. Current hardware, however, sets stringent
limitations on how long such simulations can run before decoherence begins to
corrupt results. The Jarzynski equality, a fluctuation theorem that allows for
the computation of equilibrium free energy differences from an ensemble of
short, non-equilibrium dynamics simulations, can make use of such short-time
simulations on quantum computers. Here, we present a quantum algorithm based on
the Jarzynski equality for computing free energies of quantum materials. We
demonstrate our algorithm using the transverse field Ising model on both a
quantum simulator and real quantum hardware. As the free energy is a central
thermodynamic property that allows one to compute virtually any equilibrium
property of a physical system, the ability to perform this algorithm for larger
quantum systems in the future has implications for a wide range of applications
including the construction of phase diagrams, prediction of transport
properties and reaction constants, and computer-aided drug design
Recommended from our members
What Levels of Coupled Cluster Theory Are Appropriate for Transition Metal Systems? A Study Using Near-Exact Quantum Chemical Values for 3d Transition Metal Binary Compounds.
Transition metal compounds are traditionally considered to be challenging for standard quantum chemistry approximations like coupled cluster (CC) theory, which are usually employed to validate lower level methods like density functional theory (DFT). To explore this issue, we present a database of bond dissociation energies (BDEs) for 74 spin states of 69 diatomic species containing a 3d transition metal atom and a main group element, in the moderately sized def2-SVP basis. The presented BDEs appear to have an (estimated) 3Ï error less than 1 kJ/mol relative to the exact solutions to the nonrelativistic Born-Oppenheimer Hamiltonian. These benchmark values were used to assess the performance of a wide range of standard single reference CC models, as the results should be beneficial for understanding the limitations of these models for transition metal systems. We find that interactions between metals and monovalent ligands like hydride and fluoride are well described by CCSDT. Similarly, CCSDTQ appears to be adequate for bonds between metals and nominally divalent ligands like oxide and sulfide. However, interactions with polyvalent ligands like nitride and carbide are more challenging, with even CCSDTQ(P)Î yielding errors on the scale of a few kJ/mol. We also find that many perturbative and iterative approximations to higher order terms either yield disappointing results or actually worsen the performance relative to the baseline low level CC method, indicating that complexity does not always guarantee accuracy