Phys. Chem. Chem. Phys. 2020, published on the web (DOI: 10.1039/D0CP03745A) Open access A probabilistic spin annihilation method based on the quantum phase estimation algorithm is presented for quantum chemical calculations on quantum computers. This approach can eliminate more than one spin component from the spin contaminated wave functions by single operation. Comparison with the spin annihilation operation on classical computers is given.

### Category: publications

## Trityl-Aryl-Nitroxide-Based Genuinely gEngineered Biradicals, As Studied by Dynamic Nuclear Polarization Multifrequency ESR/ENDOR, Arbitrary Wave Generator Pulse Microwave Waveform Spectroscopy, and Quantum Chemical Calculations

J. Phys. Chem. A 2019, 123, 7507-7517. (DOI: 10.1021/acs.jpca.9b07169) Trityl and nitroxide radicals are connected by π-topologically controlled aryl linkers, generating genuinely g-engineered biradicals. They serve as a typical model for biradicals in which the exchange (J) and hyperfine interactions compete with the g-difference electronic Zeeman interactions. The magnetic properties underlying the biradical spin Hamiltonian for solution, including J’s, have been determined by multifrequency CW-ESR and 1H ENDOR spectroscopy and compared with those obtained by quantum chemical calculations. The experimental J values were in good agreement with the quantum chemical calculations. The g-engineered biradicals have been tested as a prototype for AWG (Arbitrary Wave Generator)-based spin manipulation techniques, which enable GRAPE […]

## Quantum chemistry on quantum computers: quantum simulations of the time evolution of wave functions under the S^{2} operator and determination of the spin quantum number *S*

Phys. Chem. CHem. Phys. 2019, 21, 15356-15361. (DOI: 10.1039/C9CP02546D) Open access [ a 2019 PCCP HOT Article ] Quantum computers have an enormous impact on quantum chemical calculations. Approaches to calculate the energies of atoms and molecules on quantum computers by utilizing quantum phase estimation (QPE) and the variational quantum eigensolver (VQE) have been well documented, and dozens of methodological improvements to decrease computational costs and to mitigate errors have been reported until recently. However, the possible methodological implementation of observables on quantum computers such as calculating the spin quantum numbers of arbitrary wave functions, which is a crucial issue in quantum chemistry, has been discussed less. Here, we propose a […]

## Quantum Chemistry on Quantum Computers: A Method for Preparation of Multiconfigurational Wave Functions on Quantum Computers without Performing Post-Hartree–Fock Calculations

ACS Cent. Sci. 2019, 5, pp.167-175 (DOI: 10.1021/acscentsci.8b00788) Open access The full configuration interaction (full-CI) method is capable of providing the numerically best wave functions and energies of atoms and molecules within basis sets being used, although it is intractable for classical computers. Quantum computers can perform full-CI calculations in polynomial time against the system size by adopting a quantum phase estimation algorithm (QPEA). In the QPEA, the preparation of initial guess wave functions having sufficiently large overlap with the exact wave function is recommended. The Hartree–Fock (HF) wave function is a good initial guess only for closed shell singlet molecules and high-spin molecules carrying no spin-β unpaired electrons, around […]

## Open shell electronic state calculations on quantum computers: A quantum circuit for the preparation of configuration state functions based on Serber construction

Chemical Physics Letters: X 2019, 1, 10002. (DOI: 10.1016/j.cpletx.2018.100002) Open access Full configuration interaction (full-CI) calculations can be executed efficiently on quantum computers (QCs) by utilizing a quantum phase estimation algorithm (QPEA). In the QPEA-based full-CI on QCs, the preparation of the initial guess wave functions having large overlap with the full-CI root is crucial. Recently, we proposed a quantum circuit to prepare spin symmetry-adapted configuration state functions (CSFs) toward open shell electronic structure calculations of molecules on QCs. Here, we propose an improved quantum circuit, based on Serber construction of spin eigenfunctions, enabling us to prepare CSFs with much less and easier-to-implement quantum gates than the previously proposed one. […]

## Microscopic Behavior of Active Materials inside a TCNQ-based Lithium Ion Rechargeable Battery by in-situ 2D ESR Measurements

ACS Appl. Mater. Interfaces 10, pp.43631-43640 (2018) (DOI: 10.1021/acsami.8b14967) Real-time spectroscopic measurements in rechargeable batteries are important to understand the electrochemistry of the batteries at the molecular level and improve relevant functionalities. We have applied in-situ two-dimensional (2D) ESR spectroscopy to a well-known organic lithium ion battery, which is composed of 7,7,8,8-tetracyanoquinodimethane (TCNQ) as the cathode-active material and a lithium metal anode electrode. The TCNQ rechargeable battery is suitable for investigating electrochemistry in the battery in terms of behavior of electron spin at microscopic levels on both the cathode and anode electrodes. We have discussed two-stage oxidation/reduction reactions of TCNQ, Li deposited/stripped process and their resulting dendritic and/or mossy microstructures, clearly elucidating the cause […]

## ESR analyses of picket fence MnII and 6th ligand coordinated FeIII porphyrins (S = 5/2) and a CoII(hfac) complex (S = 3/2) with sizable ZFS parameters revisited: a full spin Hamiltonian approach and quantum chemical calculations

Dalton Trans., 47, 16429-16444 (2018). (DOI:10.1039/C8DT02988A) The fictitious spin-1/2 (effective spin-1/2) Hamiltonian approach has been the putative method to analyze the conventional fine-structure/hyperfine ESR spectra of high spin metallocomplexes with sizable zero-field splitting (ZFS) tensors since the early 1950s, and the approach gives salient principal geff-values far from g = 2 without explicitly affording their ZFS values in most cases. The experimental geff-values thus determined, however, never agree with those (gtrue-values) of the true principal g-tensors, which are obtainable from reliable quantum chemical calculations. We have recently derived exact or extremely accurate analytical expressions for the geff/gtrue relationships for the spin quantum number S‘s up to S = 7/2 (T. […]

## Reversible solution pi-dimerization and long multicenter bonding in a stable phenoxyl radical

Chemistry – A European Journal Chem. Eur. Journal, 24, pp.14906-14910 (2018). (DOI:10.1002/chem.201802204) Reversible solution p-dimerization is observed in the stable neutral phenoxyl radical 2,6-bis-(8-quinolylamino)-4-(tertbutyl) phenoxyl baqp and is spectroscopically characterized. This behavior, not previously observed for p-extended phenoxyl radicals, is relevant to the formation of long multicenter bonding in the p-dimer at low temperature akin to previously reported phenalenyl radicals. Our experimental data are supported in a quantitative manner by results from density functional theory (DFT) and ab initio molecular orbital theory calculations. Our theoretical results indicate that the solution dimer features strong bonding interactions between the two phenoxyl rings but that the stability of the dimer is also related […]

## Fe-Transferrins or their homologues in ex-vivo mushrooms as identified by ESR spectroscopy and quantum chemical calculations: a full spin-Hamiltonian approach for the ferric sextet state with intermediate zero-field splitting parameters

Food Chemistry Volume 266, 15 November 2018, Pages 24-30 http://doi.org/10.1016/j.foodchem.2018.05.092 Fe-transferrins/their homologues in ex-vivo mushrooms were identified by ESR spectroscopy at liquid helium temperature, 4 K. The ESR fine-structure signals from Grifola frondosa were analyzed by spectral simulation with a full spin-Hamiltonian approach, determining the spin Hamiltonian parameters of the ferric iron species bound in the biological environment: S = 5/2, g = (2.045, 2.01, 2.235), |D| = 0.28 cm−1, |E/D| = 0.05. The zero-field splitting (ZFS) parameters, D– and E-values, are very close to the reported values, |D| = 0.25 cm−1 and |E/D| = 0.06, for an Fe-transferrin with oxalate anion, and to |D| = 0.25 cm−1 and |E/D| = 0.04 for one with malonate anion in human sera, suggesting that the Fe3+ species are from Fe-transferrins or their […]

## Using optimal control methods with constraints to generate singlet states in NMR

J. Magn. Reson., 291, pp.14-22 (2018). DOI:10.1016/j.jmr.2018.03.005 A method is proposed for optimizing the performance of the APSOC (Adiabatic-Passage Spin Order Conversion) technique, which can be exploited in NMR experiments with singlet spin states. In this technique magnetization-to-singlet conversion (and singlet-to-magnetization conversion) is performed by using adiabatically ramped RF-fields. Optimization utilizes the GRAPE (Gradient Ascent Pulse Engineering) approach, in which for a fixed search area we assume monotonicity to the envelope of the RF-field. Such an approach allows one to achieve much better performance for APSOC; consequently, the efficiency of magnetization-to-singlet conversion is greatly improved as compared to simple model RF-ramps, e.g., linear ramps. We also demonstrate that the optimization […]