Spin-resolved momentum densities: probing orbitals in magnetic oxides

Studies of spin-resolved electron momentum densities involve the measurement of the so-called magnetic Compton profile. This is a one-dimensional projection of the electron momentum distribution of only those electrons that contribute to the spin moment of a sample. The technique is applicable to ferri- and ferromagnetic materials. Since electrons originating from different atomic orbitals have specific momentum densities, it is often possible to determine the origin of the magnetism present. Typically, interpretation requires the use of electronic structure calculations using molecular orbital and band structure approaches. The profile is obtained experimentally via the inelastic "Compton" scattering of high energy X-rays. For the experiments discussed here, the high energy beamlines at the ESRF and SPring-8 synchrotron X-ray sources were used, where we have a cryomagnet which can provide a sample environment with applied magnetic fields up to 9 Tesla, at temperatures from 1.3K to 600K. In this talk, we discuss our combined experimental and theoretical study of the spin density of the low-dimensional frustrated metamagnet Ca3Co2O6. The spin moment, measured using magnetic Compton scattering, confirms the existence of a large unquenched Co orbital moment (1.310.1 μB). With regards to the orbital occupation, we have performed molecular orbital calculations on the active trigonal CoO6cluster in order to determine which Co 3d orbitals are responsible for the observed electronic and magnetic behaviour and the observed orbital moment, and revealing the existence a oxygen spin moment of approximately 0.9 μB. Electronic structure calculations with a Hubbard U energy term give Compton profiles which are in good agreement with our experimental data. The magnetic Compton profile exhibits oscillations, which are well described, and their frequency in momentum space corresponds to the real-space inter-cobalt site bond length.

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Electronic Structure Calculations on a Real-Space Mesh with Multigrid Acceleration

MRS Proceedings ◽

10.1557/proc-408-145 ◽

1995 ◽

Vol 408 ◽

Author(s):

D. J. Sullivan ◽

E. L. Briggs ◽

C. J. Brabec ◽

J. Bernholc

Keyword(s):

Electronic Structure ◽

Ab Initio ◽

Large Scale ◽

Electronic Structure Calculations ◽

High Energy ◽

Real Space ◽

Parallel Architectures ◽

Wurtzite Phase ◽

Ongoing Work ◽

Structure Calculations

AbstractWe have developed a set of techniques for performing large scale ab initio calculations using multigrid accelerations and a real-space grid as a basis. The multigrid methods permit efficient calculations on ill-conditioned systems with long length scales or high energy cutoffs. We discuss the design of pseudopotentials for real-space grids, and the computation of ionic forces. The technique has been applied to several systems, including an isolated C60 molecule, the wurtzite phase of GaN, a 64-atom cell of GaN with the Ga d-states in valence, and a 443-atom protein. The method has been implemented on both vector and parallel architectures. We also discuss ongoing work on O(N) implementations and solvated biomolecules.

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Electronic Structure Calculations of the Copper Oxygen Planes in Yba2Cu3O6+δ, for 0 < δ < 1

MRS Proceedings ◽

10.1557/proc-169-37 ◽

1989 ◽

Vol 169 ◽

Author(s):

J. A. Cogordan

Keyword(s):

Electronic Structure ◽

Excited State ◽

Ab Initio ◽

Molecular Orbital ◽

Lower Energy ◽

Closed Shell ◽

Electronic Structure Calculations ◽

Open Shell ◽

Molecular Orbitals ◽

Structure Calculations

AbstractMolecular ab initio seIf-consistent calculations on clusters simulating the copper-oxygen layers in the Yba2Cu3O6;δ are reported. The electronic structure, of this layer, was computed for different sets of values of the lattice parameters (a,b,c), according to their dependence on the oxygen stiochiometry. For the molecular orbitals , two different electronic occupations are considered, a closed shell and an open shell. For the open shell, an electron has been excited to the first virtual molecular orbital. It is found that this excited state has lower energy than the closed shell configuration for 0 < δ < 1. Molecular energies an electronic population are reported.

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Compton Scattering from Heavier Metals

Zeitschrift für Naturforschung A ◽

10.1515/zna-1993-1-261 ◽

1993 ◽

Vol 48 (1-2) ◽

pp. 334-342 ◽

Cited By ~ 2

Author(s):

B. K Sharma

Keyword(s):

Electronic Structure ◽

Compton Scattering ◽

Three Dimensional ◽

Ion Beams ◽

Compton Profile ◽

Good Resolution ◽

Dimensional Electron ◽

Electron Momentum ◽

Momentum Distributions

Abstract The use of Compton scattering in the determination of electronic structure has grown considerably in the last two decades. With the advent of synchrotron radiation it has become possible, even with good resolution, to measure several single-crystal orientations to determine three-dimensional electron momentum distributions. Although most of the earlier work has been directed to low-Z materials, in the last few years medium and high-Z metals have also been investigated with this technique. In this paper we present a review of these studies on heavier metals with particular attention to the difficulties encountered. Compton profile measurements from techniques based on energetic ion beams are also considered briefly.

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Electronic structure calculations of positron lifetimes in nuclear materials: SiC and UO2

SNA + MC 2013 - Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo ◽

10.1051/snamc/201401312 ◽

2014 ◽

Author(s):

Julia Wiktor ◽

Gérald Jomard ◽

Michel Freyss ◽

Marjorie Bertolus

Keyword(s):

Electronic Structure ◽

Electronic Structure Calculations ◽

Nuclear Materials ◽

Positron Lifetimes ◽

Structure Calculations

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Message Passing Neural Networks for Partial Charge Assignment to Metal-Organic Frameworks

10.26434/chemrxiv.12298487 ◽

2020 ◽

Author(s):

Ali Raza ◽

Arni Sturluson ◽

Cory Simon ◽

Xiaoli Fern

Keyword(s):

Electronic Structure ◽

Message Passing ◽

Gas Adsorption ◽

Metal Organic Frameworks ◽

Computational Cost ◽

Electronic Structure Calculations ◽

High Fidelity ◽

Partial Charges ◽

Metal Organic ◽

Structure Calculations

Virtual screenings can accelerate and reduce the cost of discovering metal-organic frameworks (MOFs) for their applications in gas storage, separation, and sensing. In molecular simulations of gas adsorption/diffusion in MOFs, the adsorbate-MOF electrostatic interaction is typically modeled by placing partial point charges on the atoms of the MOF. For the virtual screening of large libraries of MOFs, it is critical to develop computationally inexpensive methods to assign atomic partial charges to MOFs that accurately reproduce the electrostatic potential in their pores. Herein, we design and train a message passing neural network (MPNN) to predict the atomic partial charges on MOFs under a charge neutral constraint. A set of ca. 2,250 MOFs labeled with high-fidelity partial charges, derived from periodic electronic structure calculations, serves as training examples. In an end-to-end manner, from charge-labeled crystal graphs representing MOFs, our MPNN machine-learns features of the local bonding environments of the atoms and learns to predict partial atomic charges from these features. Our trained MPNN assigns high-fidelity partial point charges to MOFs with orders of magnitude lower computational cost than electronic structure calculations. To enhance the accuracy of virtual screenings of large libraries of MOFs for their adsorption-based applications, we make our trained MPNN model and MPNN-charge-assigned computation-ready, experimental MOF structures publicly available.<br>

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