On the accuracy of the state space restriction approximation for spin dynamics simulations

Karabanov, Alexander; Kuprov, Ilya; Charnock, G. T. P.; Drift, Anniek van der; Edwards, Luke; Köckenberger, Walter

doi:10.1063/1.3624564

Cited by 38 publications

(45 citation statements)

References 29 publications

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“…The size of these systems are of course limited by computer memory restrictions, although solutions for overcoming these limitations are currently being proposed [17,18]. Based on such calculations we suggested in a recent publication [12,15] that the presence of many (core) nuclei, which are directly hyperfine coupled to the electrons taking part in the SE and CE mechanisms, broaden the double quantum (DQ) and zero quantum (ZQ) spectra, and dramatically reduce the end polarization.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Aspects of Dynamic Nuclear Polarization in the Solid State: The Influence of High Radical Concentrations on the Solid Effect and Cross Effect Mechanisms

et al. 2012

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Dynamic nuclear polarization (DNP) is used to enhance signals in NMR and MRI experiments. During these experiments microwave (MW) irradiation mediates transfer of spin polarization from unpaired electrons to their neighboring nuclei. Solid state DNP is typically applied to samples containing high concentrations (i.e. 10-40 mM) of stable radicals that are dissolved in glass forming solvents together with molecules of interest. Three DNP mechanisms can be responsible for enhancing the NMR signals: the solid effect (SE), the cross effect (CE), and thermal mixing (TM). Recently, numerical simulations were performed to describe the SE and CE mechanisms in model systems composed of several nuclei and one or two electrons. It was shown that the presence of core nuclei, close to DNP active electrons, can result in a decrease of the nuclear polarization, due to broadening of the double quantum (DQ) and zero quantum (ZQ) spectra. In this publication we consider samples with high radical concentrations, exhibiting broad inhomogeneous EPR line-shapes and slow electron cross-relaxation rates, where the TM mechanism is not the main source for the signal enhancements. In this case most of the electrons in the sample are not affected by the MW field applied at a discrete frequency. Numerical simulations are performed on spin systems composed of several electrons and nuclei in an effort to examine the role of the DNP inactive electrons. Here we show that these electrons also broaden the DQ and ZQ spectra, but that they hardly cause any loss to the DNP enhanced nuclear polarization due to their spinlattice relaxation mechanism. Their presence can also prevent some of the polarization losses due to the core nuclei.

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Section: Introductionmentioning

confidence: 99%

Theoretical Aspects of Dynamic Nuclear Polarization in the Solid State: The Influence of High Radical Concentrations on the Solid Effect and Cross Effect Mechanisms

et al. 2012

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“…Karabanov and co-workers 13 discussed the topic of state space restriction approximation in simulations of spin dynamics, of interest for NMR, EPR and dynamic nuclear polarization (DNP). The main assumption of the approximation is that a typical spin state trajectory for a large spin system will during its time evolution only visit a limited subspace of the total state space.…”

Section: Introductionmentioning

confidence: 99%

Nuclear spin relaxation in liquids and gases

Kowalewski¹

2013

Nuclear Magnetic Resonance

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This report reviews the progress in the field of NMR relaxation in fluids. The emphasis is on comparatively simple liquids and solutions of physico-chemical and chemical interest, in analogy with the previous periods, but selected biophysicsrelated topics and relaxation-related work on more complex systems (macromolecular solutions, liquid crystalline systems, glassy and porous materials) are also covered. The period under review is from June 2011 through May 2012. Some earlier works, overlooked in last year's chapter, are also included. The outline of this chapter is as follows: section 2 which follows the introduction covers the general, physical and experimental aspects of nuclear spin relaxation in liquids and is further divided in seven subsections. The first two are fairly general and the following three discuss more specific aspects of spin-1/2 systems. The last two subsections cover quadrupolar nuclei and paramagnetic systems, respectively. Section 3 deals with applications of NMR relaxation in liquids, starting with pure liquids and continuing with solutions of low-molecular weight compounds. It also includes a selection of works on solutions of biological macromolecules and other complex systems. The progress in the field of relaxation in gases is described in section 4.

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“…In practical simulations the overall amount of work ends up being smaller because non-Hermitian density matrices are used to replace phase cycles, which are typically 8 to 16 simulations long. It is also often the case (particularly in weakly coupled spin systems) that the density matrix has many small singular values, which may be ignored altogether, thus reducing the amount of work in Equation (8).…”

Section:  0mentioning

confidence: 99%

“…The fact that this number grows polynomially with the number of spins has profound algebraic and physical consequences elsewhere 8,12 , but in our current context it may be used to get an upper bound on the density of the matrices (the ratio of the number of non-zeros to the total number of elements) involved in numerical spin dynamics simulations. The resulting bounds may then be used to obtain asymptotic estimates on the storage, communication and computation requirements.…”

Section: Computation Storage and Communication Overheadsmentioning

confidence: 99%

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Parallel density matrix propagation in spin dynamics simulations

Edwards

Kuprov

2012

The Journal of Chemical Physics

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Several methods for density matrix propagation in distributed computing environments, such as clusters and graphics processing units, are proposed and evaluated. It is demonstrated that the large communication overhead associated with each propagation step (two-sided multiplication of the density matrix by an exponential propagator and its conjugate) may be avoided and the simulation recast in a form that requires virtually no inter-thread communication. Good scaling is demonstrated on a 128-core (16 nodes, 8 cores each) cluster.

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On the accuracy of the state space restriction approximation for spin dynamics simulations

Cited by 38 publications

References 29 publications

Theoretical Aspects of Dynamic Nuclear Polarization in the Solid State: The Influence of High Radical Concentrations on the Solid Effect and Cross Effect Mechanisms

Theoretical Aspects of Dynamic Nuclear Polarization in the Solid State: The Influence of High Radical Concentrations on the Solid Effect and Cross Effect Mechanisms

Nuclear spin relaxation in liquids and gases

Parallel density matrix propagation in spin dynamics simulations

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