scholarly journals Insights in Magnetodynamics from a Simple Two-Level Model

2020 ◽  
Author(s):  
Stanislav Avdoshenko ◽  
Rajyavardhan Ray
Keyword(s):  
Density Matrix ◽  
Single Molecule ◽  
Quantum Dynamics ◽  
Single Molecule Magnets ◽  
Recent Contribution ◽  
Level Model ◽  
Theory Of Optimal Control ◽  
Reduced Density ◽  
And Control ◽  
Manipulation And Control

With single-molecule magnets research on the rise as a result of recent advantages in the field, like remarkable high blocking temperatures up to 60 Kelvin [Nature, 548, 439, 2017], gigantic coercivity up to 80 Tesla [Nat Commun., 10, 571, 2019], magnetization stability in the thin films, further applications are seriously in the scope. The possible venue here is to develop a theory of magnetic moment manipulation and control at the microscopic level. Theory of optimal control in quantum dynamics in complex systems is well-developed. For example, the uses of density matrix techniques have been well summarized already in the early ‘60s by Fano, Haar, and many others. Thus, in many respects, the task is to reframe that research into the language of the problem at hand, and into familiar terms for the community. Recently, it was already proven the Redfield reduced density matrix techniques are applicable for slow-relaxing single-molecule magnets [Nat Commun., 8, 14620, 2017]. In our recent contribution[PCCP,20, 11656, 2018], we have outlined the use of Lindblad dynamics in combination with a few axioms in the rationalization of the relaxation behavior of single-molecule magnets. In this report we put this approach in the context of the magentodynamics theory, showing the close connection to the Landau-Lifshitz-Gilbert model and presenting further elaboration for the proposed method.

scholarly journals Insights in Magnetodynamics from a Simple Two-Level Model

2020 ◽  
Author(s):  
Stanislav Avdoshenko ◽  
Rajyavardhan Ray
Keyword(s):  
Density Matrix ◽  
Single Molecule ◽  
Quantum Dynamics ◽  
Single Molecule Magnets ◽  
Recent Contribution ◽  
Level Model ◽  
Theory Of Optimal Control ◽  
Reduced Density ◽  
And Control ◽  
Manipulation And Control

With single-molecule magnets research on the rise as a result of recent advantages in the field, like remarkable high blocking temperatures up to 60 Kelvin [Nature, 548, 439, 2017], gigantic coercivity up to 80 Tesla [Nat Commun., 10, 571, 2019], magnetization stability in the thin films, further applications are seriously in the scope. The possible venue here is to develop a theory of magnetic moment manipulation and control at the microscopic level. Theory of optimal control in quantum dynamics in complex systems is well-developed. For example, the uses of density matrix techniques have been well summarized already in the early ‘60s by Fano, Haar, and many others. Thus, in many respects, the task is to reframe that research into the language of the problem at hand, and into familiar terms for the community. Recently, it was already proven the Redfield reduced density matrix techniques are applicable for slow-relaxing single-molecule magnets [Nat Commun., 8, 14620, 2017]. In our recent contribution[PCCP,20, 11656, 2018], we have outlined the use of Lindblad dynamics in combination with a few axioms in the rationalization of the relaxation behavior of single-molecule magnets. In this report we put this approach in the context of the magentodynamics theory, showing the close connection to the Landau-Lifshitz-Gilbert model and presenting further elaboration for the proposed method.

scholarly journals Quantum dynamics of exchange biased single-molecule magnets

2004 ◽  
Vol 272-276 ◽  
pp. 1037-1041 ◽  
Author(s):  
W. Wernsdorfer ◽  
N. Aliaga-Alcalde ◽  
R. Tiron ◽  
D.N. Hendrickson ◽  
G. Christou
Keyword(s):  
Single Molecule ◽  
Quantum Dynamics ◽  
Single Molecule Magnets

Molecular nanomagnets

2017 ◽  
Author(s):  
W. Wernsdorfer
Keyword(s):  
Molecular Electronics ◽  
Single Molecule ◽  
Quantum Dynamics ◽  
Spin Model ◽  
Photon Absorption ◽  
Single Molecule Magnets ◽  
Molecular Nanomagnets ◽  
Quantum Properties ◽  
Molecular Spintronics ◽  
Quantum Phenomena

This article describes the quantum phenomena observed in molecular nanomagnets. Molecular nanomagnets, or single-molecule magnets (SMMs), provides a fundamental link between spintronics and molecular electronics. SMMs combine the classic macroscale properties of a magnet with the quantum properties of a nanoscale entity. The resulting field, molecular spintronics, aims at manipulating spins and charges in electronic devices containing one or more molecules. This article first considers molecular nanomagnets and the giant spin model for nanomagnets before discussing the quantum dynamics of a dimer of nanomagnets, resonant photon absorption in Cr7Ni antiferromagnetic rings, and photon-assisted tunnelling in a single-molecule magnet. It also examines environmental decoherence effects in nanomagnets and concludes by highlighting the new trends towards molecular spintronics using junctions and nano-SQUIDs.

Extension of Frozen Natural Orbital Approximation to Open-Shell References: Theory, Implementation, and Application to Single-Molecule Magnets

2019 ◽  
Author(s):  
Pavel Pokhilko ◽  
Daniil Izmodenov ◽  
Anna I. Krylov
Keyword(s):  
Density Matrix ◽  
Single Molecule ◽  
Open Shell ◽  
State Density ◽  
Molecular Orbitals ◽  
The State ◽  
Wave Functions ◽  
Virtual Space ◽  
Single Molecule Magnets ◽  
Natural Orbitals

Natural orbitals are often used in quantum chemistry to achieve a more compact representation of correlated wave-functions. Using natural orbitals computed as eigenstates of the virtual-virtual block of the state density matrix instead of the canonical Hartree-Fock molecular orbitals results in smaller errors when the same fraction of virtual orbitals is frozen. This strategy, termed frozen natural orbitals (FNO) approach, has been successfully used to reduce the cost of state-specific coupled-cluster (CC) calculations, such as ground-state CC, as well as some multi-state methods, i.e., EOM-IP-CC (equation-of-motion CC method for ionization potentials). This contribution extends the FNO approach to the EOM-SF-CC ansatz (EOM-CC with spin-flip), which has been developed to describe certain multi-configurational wave-functions within the single-reference framework. In contrast to EOM-IP-CCSD, which describes open-shell target states by using a closed-shell reference, EOM-SF-CCSD relies on high-spin open-shell references (triplets, quartets, etc). Consequently, straightforward application of FNOs computed for an open-shell reference leads to an erratic behavior of the EOM-SF-CC energies and properties, which can be attributed to an inconsistent truncation of the α and β orbital spaces. A general solution to problems arising in the EOM-CC calculations utilizing open-shell references, termed OSFNO (open-shell FNO), is proposed. The OSFNO algo-rithm first identifies corresponding orbitals by means of singular value decomposition (SVD) of the overlap matrix of the α and β molecular orbitals and determines virtual orbitals corresponding to the singly occupied space. This is followed by SVD of the singlet part of the state density matrix in the remaining virtual orbital subspace. The so-computed FNOs preserve the spin purity of the open-shell orbital subspace to the extent allowed by the original reference thus facilitating a safe truncation of the virtual space. The performance of the OSFNO approximation in combination with different choices of reference orbitals is benchmarked for a set of diradicals and triradicals. For a set of di-copper single-molecule magnets, a conservative truncation criterion corresponding to a two-fold reduction of the virtual space in a triple-zeta basis leads to errors of 5–18 cm<sup>-1</sup> in the singlet–triplet gaps and errors of ∼2-3 cm<sup>-1</sup> in the spin–orbit coupling constants.

Current-constrained one-electron reduced density-matrix theory for non-equilibrium steady-state molecular conductivity

2019 ◽  
Vol 21 (23) ◽  
pp. 12620-12624 ◽  
Author(s):  
Alexandra E. Raeber ◽  
David A. Mazziotti
Keyword(s):  
Steady State ◽  
Density Matrix ◽  
Single Molecule ◽  
Matrix Theory ◽  
Electronic Devices ◽  
Reduced Density Matrix ◽  
Circuit Elements ◽  
Reduced Density ◽  
Density Matrix Theory ◽  
Non Equilibrium

In the effort to create ever smaller electronic devices, the idea of single molecule circuit elements has sparked the imagination of scientists for nearly fifty years.

scholarly journals Attempting to understand (and control) the relationship between structure and magnetism in an extended family of Mn6 single-molecule magnets

2009 ◽  
pp. 3403 ◽  
Author(s):  
Ross Inglis ◽  
Leigh F. Jones ◽  
Constantinos J. Milios ◽  
Saiti Datta ◽  
Anna Collins ◽  
...  
Keyword(s):  
Single Molecule ◽  
Extended Family ◽  
Single Molecule Magnets ◽  
And Control ◽  
The Relationship

Extension of Frozen Natural Orbital Approximation to Open-Shell References: Theory, Implementation, and Application to Single-Molecule Magnets

2019 ◽  
Author(s):  
Pavel Pokhilko ◽  
Daniil Izmodenov ◽  
Anna I. Krylov
Keyword(s):  
Density Matrix ◽  
Single Molecule ◽  
Open Shell ◽  
State Density ◽  
Molecular Orbitals ◽  
The State ◽  
Wave Functions ◽  
Virtual Space ◽  
Single Molecule Magnets ◽  
Natural Orbitals

Natural orbitals are often used in quantum chemistry to achieve a more compact representation of correlated wave-functions. Using natural orbitals computed as eigenstates of the virtual-virtual block of the state density matrix instead of the canonical Hartree-Fock molecular orbitals results in smaller errors when the same fraction of virtual orbitals is frozen. This strategy, termed frozen natural orbitals (FNO) approach, has been successfully used to reduce the cost of state-specific coupled-cluster (CC) calculations, such as ground-state CC, as well as some multi-state methods, i.e., EOM-IP-CC (equation-of-motion CC method for ionization potentials). This contribution extends the FNO approach to the EOM-SF-CC ansatz (EOM-CC with spin-flip), which has been developed to describe certain multi-configurational wave-functions within the single-reference framework. In contrast to EOM-IP-CCSD, which describes open-shell target states by using a closed-shell reference, EOM-SF-CCSD relies on high-spin open-shell references (triplets, quartets, etc). Consequently, straightforward application of FNOs computed for an open-shell reference leads to an erratic behavior of the EOM-SF-CC energies and properties, which can be attributed to an inconsistent truncation of the α and β orbital spaces. A general solution to problems arising in the EOM-CC calculations utilizing open-shell references, termed OSFNO (open-shell FNO), is proposed. The OSFNO algo-rithm first identifies corresponding orbitals by means of singular value decomposition (SVD) of the overlap matrix of the α and β molecular orbitals and determines virtual orbitals corresponding to the singly occupied space. This is followed by SVD of the singlet part of the state density matrix in the remaining virtual orbital subspace. The so-computed FNOs preserve the spin purity of the open-shell orbital subspace to the extent allowed by the original reference thus facilitating a safe truncation of the virtual space. The performance of the OSFNO approximation in combination with different choices of reference orbitals is benchmarked for a set of diradicals and triradicals. For a set of di-copper single-molecule magnets, a conservative truncation criterion corresponding to a two-fold reduction of the virtual space in a triple-zeta basis leads to errors of 5–18 cm<sup>-1</sup> in the singlet–triplet gaps and errors of ∼2-3 cm<sup>-1</sup> in the spin–orbit coupling constants.

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