High-spin Model Research Articles

Two-dimensional coherent spectrum of high-spin models via a quantum computing approach

We present and benchmark a quantum computing approach to calculate the two-dimensional coherent spectrum (2DCS) of high-spin models. Our approach is based on simulating their real-time dynamics in the presence of several magnetic field pulses, which are spaced in time. We utilize the adaptive variational quantum dynamics simulation algorithm for the study due to its compact circuits, which enables simulations over sufficiently long times to achieve the required resolution in frequency space. Specifically, we consider an antiferromagnetic quantum spin model that incorporates Dzyaloshinskii-Moriya interactions and single-ion anisotropy. The obtained 2DCS spectra exhibit distinct peaks at multiples of the magnon frequency, arising from transitions between different eigenstates of the unperturbed Hamiltonian. By comparing the one-dimensional coherent spectrum with 2DCS, we demonstrate that 2DCS provides a higher resolution of the energy spectrum. We further investigate how the quantum resources scale with the magnitude of the spin using two different binary encodings of the high-spin operators: the standard binary encoding and the Gray code. At low magnetic fields both encodings require comparable quantum resources, but at larger field strengths the Gray code is advantageous. Numerical simulations for spin models with increasing number of sites indicate a polynomial system-size scaling for quantum resources. Lastly, we compare the numerical 2DCS with experimental results on a rare-earth orthoferrite system. The observed strength of the magnonic high-harmonic generation signals in the 2DCS of the quantum high-spin model aligns well with the experimental data, showing significant improvement over the corresponding mean-field results.

Time-Resolved X-ray Emission Spectroscopy and Synthetic High-Spin Model Complexes Resolve Ambiguities in Excited-State Assignments of Transition-Metal Chromophores: A Case Study of Fe-Amido Complexes.

To fully harness the potential of abundant metal coordination complex photosensitizers, a detailed understanding of the molecular properties that dictate and control the electronic excited-state population dynamics initiated by light absorption is critical. In the absence of detectable luminescence, optical transient absorption (TA) spectroscopy is the most widely employed method for interpreting electron redistribution in such excited states, particularly for those with a charge-transfer character. The assignment of excited-state TA spectral features often relies on spectroelectrochemical measurements, where the transient absorption spectrum generated by a metal-to-ligand charge-transfer (MLCT) electronic excited state, for instance, can be approximated using steady-state spectra generated by electrochemical ligand reduction and metal oxidation and accounting for the loss of absorptions by the electronic ground state. However, the reliability of this approach can be clouded when multiple electronic configurations have similar optical signatures. Using a case study of Fe(II) complexes supported by benzannulated diarylamido ligands, we highlight an example of such an ambiguity and show how time-resolved X-ray emission spectroscopy (XES) measurements can reliably assign excited states from the perspective of the metal, particularly in conjunction with accurate synthetic models of ligand-field electronic excited states, leading to a reinterpretation of the long-lived excited state as a ligand-field metal-centered quintet state. A detailed analysis of the XES data on the long-lived excited state is presented, along with a discussion of the ultrafast dynamics following the photoexcitation of low-spin Fe(II)-Namido complexes using a high-spin ground-state analogue as a spectral model for the 5T2 excited state.

Testing AGN outflow and accretion models with C iv and He ii emission line demographics in z ≈ 2 quasars

ABSTRACT Using ≈190 000 spectra from the 17th data release of the Sloan Digital Sky Survey (SDSS), we investigate the ultraviolet emission line properties in z ≈ 2 quasars. Specifically, we quantify how the shape of C iv λ1549 and the equivalent width (EW) of He ii λ1640 depend on the black hole mass and Eddington ratio inferred from Mg ii λ2800. Above L/LEdd ≳ 0.2, there is a strong mass dependence in both C iv blueshift and He ii EW. Large C iv blueshifts are observed only in regions with both high mass and high accretion rate. Including X-ray measurements for a subsample of 5000 objects, we interpret our observations in the context of AGN accretion and outflow mechanisms. The observed trends in He ii and 2 keV strength are broadly consistent with theoretical qsosed models of AGN spectral energy distributions (SEDs) for low spin black holes, where the ionizing SED depends on the accretion disc temperature and the strength of the soft excess. High spin models are not consistent with observations, suggesting SDSS quasars at z ≈ 2 may in general have low spins. We find a dramatic switch in behaviour at L/LEdd ≲ 0.1: the ultraviolet emission properties show much weaker trends, and no longer agree with qsosed predictions, hinting at changes in the structure of the broad line region. Overall, the observed emission line trends are generally consistent with predictions for radiation line driving where quasar outflows are governed by the SED, which itself results from the accretion flow and hence depends on both the SMBH mass and accretion rate.

Domain-based local pair natural orbital CCSD(T) calculations of fourteen different S2 intermediates for water oxidation in the Kok cycle of OEC of PSII. Re-visit to one LS-two HS model for the S2 state

Domain-based local pair natural orbital (DLPNO) coupled cluster single and double (CCSD) with triple perturbation (T) correction methods were applied for fourteen different S2 structures of the CaMn4O5 cluster in oxygen evolving complex (OEC) of photosystem II (PSII). The DLPNO-CCSD(T0) calculations elucidated that the right (R)-opened S2aYZ structure (a = O2− at the O(5) site, Y = W2 and Z = W1) with the low spin (LS) (S = 1/2, g = 2) state and two left (L)-opened S2aYZ structures with the high spin (HS) (S = 5/2, g = 4; g > 4) state were nearly degenerated in energy, supporting previous one LS-two HS model for the S2 state in compatible with recent EXAFS and EPR results.

MOLECULAR STRUCTURE OF TRIS(ACETYLACETONATE)IRON STUDIED BY GAS-PHASE ELECTRON DIFFRACTION AND DFT CALCULATIONS

The molecular structure of tris(acetylacetonate)iron, Fe(O2C5H7)3, has been determined by synchronous gas-phase electron diffraction and mass spectrometric experiment along with quantum chemical calculations at the DFT/UB3LYP/cc-pVTZ theory level. The best agreement between theoretical and experimental intensity curves of scattered electrons was obtained for the high spin model with the symmetry D3 of molecule. The DFT calculations also resulted in high spin electronic state 6A1 of the molecule Fe(O2C5H7)3 as the ground one at the geometrical configuration of D3 symmetry.Forcitation:Petrova A.A., Tverdova N.V., Giricheva N.I. Girichev G.V. Molecular structure of tris(acetylacetonate)iron studied by gas-phase electron diffraction and DFT calculations. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 3. P. 97-99.

Structural Analysis of High-Spin States of S0-S4 at OEC Complex: A Theoretical Approach of Small Models

S-states at oxygen evolving complex (OEC) are widely studied due to its large importance in photo-oxidation water process. The structural aspects involving S0, S1, S2, S3 and S4 states are still not solved theoretically. Particularly, spin states have been analyzed as an important aspect in S-state models. Seeking to obtain a relevant and simple model to cover high-spin (HS) S0-S4 states we develop a 55-57 atoms model. Through quantum chemical calculations we figured out that our interatomic distance parameters are in agreement with experimental and other theoretical reference values by ca. 10.0 and 3.5%, respectively, being also in good agreement with other theoretical models containing a large number of atoms. Our HS models presented expected oxidation states according to other data on literature for small theoretical models.

Simulating Valence-to-Core X-ray Emission Spectroscopy of Transition Metal Complexes with Time-Dependent Density Functional Theory.

Valence-to-core (VtC) X-ray emission spectroscopy (XES) has emerged as a powerful technique for the structural characterization of complex organometallic compounds in realistic environments. Since the spectrum represents electronic transitions from the ligand molecular orbitals to the core holes of the metal centers, the approach is more chemically sensitive to the metal-ligand bonding character compared with conventional X-ray absorption techniques. In this paper we study how linear-response time-dependent density functional theory (LR-TDDFT) can be harnessed to simulate K-edge VtC X-ray emission spectra reliably. LR-TDDFT allows one to go beyond the single-particle picture that has been extensively used to simulate VtC-XES. We consider seven low- and high-spin model complexes involving chromium, manganese, and iron transition metal centers. Our results are in good agreement with experiment.

Modelling of thermo-chemical properties over the sub-solidus MgO–FeO binary, as a function of iron spin configuration, composition and temperature

Thermo-chemical properties and T–X phase relations diagram of the (Mg,Fe)O solid solution are modelled using mixing Helmholtz energy, ΔF(T,x)mixing, calculated by quantum mechanical and semi-empirical techniques. The sub-solidus MgO–FeO binary has been explored as a function of composition, with iron either in high-spin (HS) or low-spin (LS) configuration. Only the HS model provides physically sound results at room pressure, yielding a correct trend of cell edge versus composition, whereas LS’s issues are at variance with observations. Mixing Helmholtz energy has been parametrized by the following relationship: ΔF(T,x)mixing = x × y × [U0(T) + U1(T) × (x – y) + U2(T) × (x − y)2]−T × S(x,y)config, where y = 1−x and U j(T) are polynomials in T of the second order. ΔF(T,x)mixing exhibits a quasi-symmetric behaviour and allows one to build the T–X phase relations diagram over the MgO–FeO join. The HS model including vibrational contribution to the Helmholtz energy predicts a solid solution’s critical temperature of some 950 K, remarkably larger than olivine’s and Mg–Fe garnet’s. All this points to a more difficult Mg–Fe mixing in periclase-like structure than olivine and garnet, which, in turn, provide more structure degrees of freedom for atomic relaxation. From ΔF(T,x)mixing, we have then derived ΔH(T,x)excess and ΔS(T,x)excess. The former, characterized by a quasi-regular behaviour, has been parametrized through W × x × (1−x), obtaining W H,Mg–Fe of 17.7(5) kJ/mol. ΔS(T,x)excess, in turn, increases as a function of temperature, showing absolute figures confined within 0.1 J/mol/K. Mixing Gibbs energy, calculated combining the present issues with earlier theoretical determinations of the magnesio-wüstite’s elastic properties, has shown that the HS configuration is stable and promote Mg–Fe solid solution up to ≈15 GPa.

Photo-Induced Spin-State Conversion in Solvated Transition Metal Complexes Probed via Time-Resolved Soft X-ray Spectroscopy

Solution-phase photoinduced low-spin to high-spin conversion in the Fe(II) polypyridyl complex [Fe(tren(py)(3))](2+) (where tren(py)(3) is tris(2-pyridylmethyliminoethyl)amine) has been studied via picosecond soft X-ray spectroscopy. Following (1)A(1) --> (1)MLCT (metal-to-ligand charge transfer) excitation at 560 nm, changes in the iron L(2)- and L(3)-edges were observed concomitant with formation of the transient high-spin (5)T(2) state. Charge-transfer multiplet calculations coupled with data acquired on low-spin and high-spin model complexes revealed a reduction in ligand field splitting of approximately 1 eV in the high-spin state relative to the singlet ground state. A significant reduction in orbital overlap between the central Fe-3d and the ligand N-2p orbitals was directly observed, consistent with the expected ca. 0.2 A increase in Fe-N bond length upon formation of the high-spin state. The overall occupancy of the Fe-3d orbitals remains constant upon spin crossover, suggesting that the reduction in sigma-donation is compensated by significant attenuation of pi-back-bonding in the metal-ligand interactions. These results demonstrate the feasibility and unique potential of time-resolved soft X-ray absorption spectroscopy to study ultrafast reactions in the liquid phase by directly probing the valence orbitals of first-row metals as well as lighter elements during the course of photochemical transformations.

Two-dimensional spin-1 frustrated Heisenberg model with valence-bond ground states

In this paper, we propose a method to understand the nature of the quantum disorder phase of the two-dimensional (2D) high-spin frustrated model. The ground state and excitation properties of a fully frustrated 2D spin-1 model are studied based on a model whose ground state can be found exactly. By analogy to the pseudopotential approach in the fractional quantum Hall effect, we conclude that the ground states of the fully frustrated spin-1 model are doubly degenerate valence-bond solid (VBS) states along the horizontal or vertical direction of the square lattice. We also find that the ground state could be characterized by a nonzero string order, which rarely happened in the 2D case. The method that we used reveals the connection between the fractional quantum Hall effect and the frustrated 2D antiferromagnetism system. The VBS states capture the main character of the disordered phase in the 2D spin-1 frustrated system and can be verified by a numerical method.

Modeling hydrogen evolution from the Fe4S4 and Fe8S9X (X = N, C) clusters. Can a FeS high‐spin cluster serve as a surrogate for the FeMo cofactor?

A high-spin model of nitrogenase with a Fe(8)S(9)X(+) cluster (X = nitrogen or carbon) is used to test a mechanism for molecular hydrogen production, which is known to accompany ammonia production. The reaction proceeds with a series of protonation-reduction (PR) steps which are considered to be spontaneous if the calculated hydrogen-cluster bond energy exceeds 35-40 kcal/mol. The novel features of this mechanism include the opening of the cluster when one of the bridging sulfides undergoes two PR steps and the direct participation of the central atom when it undergoes a PR step. After the sixth PR step, a cluster is formed which has a low barrier for loss of molecular hydrogen in an exothermic reaction step. The central atom (nitrogen or carbon) has only a minor effect on the reaction steps.

Critical properties of high-spin Ising models on anisotropic lattices

The coordinates of the critical points of spin-S Ising models with coupling constants J and J′ are calculated for 1/2 ≤ S ≤ 13/2. The calculations are performed for several values of S and Δ ≡ J′/J independently by using the phenomenological renormalization-group method or (approximate) self-duality. Numerical results combined with a mean-field analysis show that the critical coupling strength for Δ ∼ 1 (weakly anisotropic lattice) is Kc(S) (Δ) = Kc(S) (1)[1 + a(1 − Δ)], where a = (d − 1)/d is independent of S (d is the space dimension). Both free energy and internal energy are determined at the critical points. An extremum of the critical internal energy is found at Δ* ∈ (0, 1). The parameter Δ* can be used as a criterion that separates quasi-isotropic and quasi-one-dimensional regimes (Δ* < Δ ≤ 1 and Δ < Δ*, respectively). The finite-size scaling amplitudes As and Ae of the inverse spin-spin and energy-energy correlation lengths are estimated. Calculations show that the amplitudes As and Ae are independent of S within the accuracy of the adopted approximations. Moreover, their ratio Ae/As is independent of the anisotropy parameter Δ. These results support the Ising universality hypothesis.

Low-Coordinate Chromium Siloxides: The “Box” [Cr(μ-Cl)(μ-OSitBu3)]4, Distorted Trigonal [(tBu3SiO)3Cr][Na(benzene)] and [(tBu3SiO)3Cr][Na(dibenzo-18-c-6)], and Trigonal (tBu3SiO)3Cr

Treatment of CrCl(2)(THF)(2) with NaOSi(t)Bu(3) afforded the tetrameric "box" [Cr(mu-Cl)(mu-OSi(t)Bu(3))](4) (1, X-ray). THF cleaved 1 to provide trans-(silox)ClCr(THF)(2) (2), whereas degradation of 1 with 4-picoline caused disproportionation and the generation of trans-Cl(2)Cr(4-pic)(2) and trans-(silox)(2)Cr(4-pic)(x) (n = 2, 3; 3, 3-4-pic). Chromous centers in 1 were antiferromagnetically coupled, and density functional calculations on the high-spin (multiplicity = 17) model [Cr(mu-Cl)(mu-OH)](4) (1') revealed that its singly occupied 3d orbitals spanned an energy range of approximately 2 eV. The addition of 8 equiv of Na(silox) to 1 yielded [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na.C(6)H(6) (4, Y shaped, angle OCrO(Na) = 91.28(7) degrees), and treatment of 4 with dibenzo-18-crown-6 produced [(silox)(3)Cr][Na(dibenzo-18-crown-6)] (5, angle OCrO = approximately 120 degrees, (120 + alpha) degrees, (120 - alpha) degrees). Calculations of [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na (4') and Cr(silox)(3)(-) (5') provided reasonable matches with the experimental geometries (X-ray). The trigonal chromic derivative (silox)(3)Cr (6) was synthesized from CrCl(3)(THF)(3) for structural and calculational comparisons to the chromous derivatives.

Temperature-induced magnetism in LaCoO3.

Polarized and unpolarized neutron measurements have been performed on ${\mathrm{LaCoO}}_{3}$ in a temperature range between 10 and 295 K. A drastic decrease in the magnetic cross section is observed below 150 K. This is the first concrete experimental evidence for the temperature-induced magnetic moment of Co ions in this oxide as proposed in the thermally populated high-spin model. The temperature dependence of the moment is in qualitative agreement with that calculated from the magnetic-susceptibility data.

ChemInform Abstract: Six‐Coordinated High‐Spin Models for Ferric Hemoproteins: NMR and ESR Study of the Diaquo(protoporphyrinato IX)iron(III) Cation and Aquohydroxo(protoporphyrinato IX)iron(III) Intercalated in Aqueous Detergent Micelles

ChemInformVolume 19, Issue 46 Organoelement Compounds ChemInform Abstract: Six-Coordinated High-Spin Models for Ferric Hemoproteins: NMR and ESR Study of the Diaquo(protoporphyrinato IX)iron(III) Cation and Aquohydroxo(protoporphyrinato IX)iron(III) Intercalated in Aqueous Detergent Micelles S. MAZUMDAR, S. MAZUMDAR Chem. Phys. Group, Tata Inst. Fundam. Res., Colaba, Bombay 400 005, IndiaSearch for more papers by this authorO. K. MEDHI, O. K. MEDHI Chem. Phys. Group, Tata Inst. Fundam. Res., Colaba, Bombay 400 005, IndiaSearch for more papers by this authorS. MITRA, S. MITRA Chem. Phys. Group, Tata Inst. Fundam. Res., Colaba, Bombay 400 005, IndiaSearch for more papers by this author S. MAZUMDAR, S. MAZUMDAR Chem. Phys. Group, Tata Inst. Fundam. Res., Colaba, Bombay 400 005, IndiaSearch for more papers by this authorO. K. MEDHI, O. K. MEDHI Chem. Phys. Group, Tata Inst. Fundam. Res., Colaba, Bombay 400 005, IndiaSearch for more papers by this authorS. MITRA, S. MITRA Chem. Phys. Group, Tata Inst. Fundam. Res., Colaba, Bombay 400 005, IndiaSearch for more papers by this author First published: November 15, 1988 https://doi.org/10.1002/chin.198846255Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume19, Issue46November 15, 1988 RelatedInformation

Six-coordinated high-spin models for ferric hemoproteins: NMR and ESR study of the diaquo(protoporphyrinato IX)iron(III) cation and aquohydroxo(protoporphyrinato IX)iron(III) intercalated in aqueous detergent micelles

Six-coordinated high-spin models for ferric hemoproteins: NMR and ESR study of the diaquo(protoporphyrinato IX)iron(III) cation and aquohydroxo(protoporphyrinato IX)iron(III) intercalated in aqueous detergent micelles

Mössbauer spectroscopy of mesohaem and protohaem myoglobins and their fluoride complexes

The Mössbauer spectra of 57Fe-enriched ferric myoglobins, pH 6, containing both protohaem and mesohaem prosthetic groups, have been measured under a variety of conditions of temperature and field. In applied fields at 4.2°K well-resolved paramagnetic hyperfine spectra are observed. These are consistent with a high-spin model with axial distortion. In small fields internal fields of order 300 kgauss are observed, corresponding to saturation fields of 493 ± 4 and 498 ± 4 kgauss for meso and proto forms, respectively. A quadrupole splitting of 0.65 ± 0.05 mm/sec is observed in each implying that the splitting in absence of magnetic interaction should be 1.3 mm/sec. This is in good agreement with the value of quadrupole splitting observed at 195°K where relaxation effects suppress magnetic interaction. The field dependence of the low temperature spectra are consistent with an axial splitting, 2 D, of 20 ± 2 cm −1, in agreement with susceptibility results. The fluoride complexes of these proteins are also high spin and have similar low temperature spectra. The saturation fields are 525 ± 3 kgauss, 2 D is 12.6 ± 1 cm −1, and the quadrupole splitting is 0.40 ± 0.05 m/sec, implying a splitting of 0.8 mm/sec in the absence of magnetic interaction. At 195°K the spectrum is unresolved as a result of residual paramagnetic effects. Again, measurements suggest that the internal field of proto form may be a few tenths of a percent higher than that of the meso form.

Phenomenological study of the new particles. Λ-particles and Λ-nuclei

Some questions on the new unstable particles are discussed, with the deliberate avoidance of any very specific assumption. The slowness of the decay rates imposes, by semi-qualitative arguments, relevant restrictions. We try to develop fully such a viewpoint, and conclusions are drawn about production processes, about processes in which the excited hyperon takes part, and about processes which occur after the capture of a heavy meson or a hyperon by a nucleus. The important question is here to know what other independent assumptions must be added to that of the long mean lives to get a consistent scheme. The Λ0-nuclei are moreover analyzed from a more phenomenological standpoint. The implications of this analysis on the high spin model of the Λ0 are discussed. The arguments, of course, are not strictly quantitative; however their possible failure would be in any case an interesting conclusion. The possible composite nature of the new particles is briefly discussed in connection with the role of weak interactions and with the possible validity of charge independence at production. Charge independence at decay is not expected to hold and this question is discussed in the case of the θ0-meson.