Assessing Relativistic Effects and Electron Correlation in the Actinide Metals Th to Pu

Density functional theory (DFT) calculations are employed to explore and assess the effects of the relativistic spin–orbit interaction and electron correlations in the actinide elements. Specifically, we address electron correlations in terms of an intra-atomic Coulomb interaction with a Hubbard U parameter (DFT + U). Contrary to recent beliefs, we show that for the ground-state properties of the light actinide elements Th to Pu, the DFT + U makes its best predictions for U = 0. Actually, our modeling suggests that the most popular DFT + U formulation leads to the wrong ground-state phase for plutonium. Instead, extending DFT and the generalized gradient approximation (GGA) with orbital–orbital interaction (orbital polarization; OP) is the most accurate approach. We believe the confusion in the literature on the subject mostly originates from incorrectly accounting for the spin–orbit (SO) interaction for the p1/2 state, which is not treated in any of the widely used pseudopotential plane-wave codes. Here, we show that for the actinides it suffices to simply discard the SO coupling for the p states for excellent accuracy. We thus describe a formalism within the projector-augmented-wave (PAW) scheme that allows for spin–orbit coupling, orbital polarization, and non-collinear magnetism, while retaining an efficient calculation of Hellmann–Feynman forces. We present results of the ground-state phases of all the light actinide metals (Th to Pu). Furthermore, we conclude that the contribution from OP is generally small, but substantial in plutonium.

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Introduction to Relativistic Quantum Chemistry

10.1093/oso/9780195140866.001.0001 ◽

2007 ◽

Cited By ~ 30

Author(s):

Kenneth G. Dyall ◽

Knut Faegri

Keyword(s):

Dirac Equation ◽

Quantum Chemistry ◽

Relativistic Theory ◽

Density Functional ◽

Relativistic Quantum ◽

Relativistic Effects ◽

Basis Sets ◽

Spin Orbit ◽

Approximate Methods ◽

Nonrelativistic Theory

This book provides an introduction to the essentials of relativistic effects in quantum chemistry, and a reference work that collects all the major developments in this field. It is designed for the graduate student and the computational chemist with a good background in nonrelativistic theory. In addition to explaining the necessary theory in detail, at a level that the non-expert and the student should readily be able to follow, the book discusses the implementation of the theory and practicalities of its use in calculations. After a brief introduction to classical relativity and electromagnetism, the Dirac equation is presented, and its symmetry, atomic solutions, and interpretation are explored. Four-component molecular methods are then developed: self-consistent field theory and the use of basis sets, double-group and time-reversal symmetry, correlation methods, molecular properties, and an overview of relativistic density functional theory. The emphases in this section are on the basics of relativistic theory and how relativistic theory differs from nonrelativistic theory. Approximate methods are treated next, starting with spin separation in the Dirac equation, and proceeding to the Foldy-Wouthuysen, Douglas-Kroll, and related transformations, Breit-Pauli and direct perturbation theory, regular approximations, matrix approximations, and pseudopotential and model potential methods. For each of these approximations, one-electron operators and many-electron methods are developed, spin-free and spin-orbit operators are presented, and the calculation of electric and magnetic properties is discussed. The treatment of spin-orbit effects with correlation rounds off the presentation of approximate methods. The book concludes with a discussion of the qualitative changes in the picture of structure and bonding that arise from the inclusion of relativity.

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GGA/PBE study of the spin isomers of Fe34,40, Co23,34, and Co12Cu Clusters with Selected Geometries

Journal of the Mexican Chemical Society ◽

10.29356/jmcs.v56i3.298 ◽

2017 ◽

Vol 56 (3) ◽

Author(s):

Faustino Aguilera-Granja ◽

Andrés Vega ◽

Luis Carlos Balbás

Keyword(s):

Ground State ◽

Density Functional ◽

Energy Difference ◽

Many Body ◽

Generalized Gradient ◽

Structural Isomers ◽

Functional Theory ◽

Ferromagnetic Ground State ◽

Spin Isomers ◽

Pseudo Potential

In a recent beam deflecting experiment was found that high and low spin states of pure Fen and Con clusters with n ≤ 300 atoms coexist at cryogenic temperatures. In this work we have studied the high spin (HS) and low spin (LS) states of several structural isomers of Co23, Co34, Fe34, and Fe40 using the generalized gradient approximation (GGA) to density functional theory as implemented in the first-principles pseudo-potential code SIESTA. The calculated energy difference between these HS and LS isomers is not consistent with the observed coexistence, which can be due to an insufficient account of many body correlation effects in the GGA description, or to unknown isomer structures of these clusters. We have calculated within the same tools the magnetic isomers of Co12Cu cluster aimed to re-visit a former DFT prediction of an anti-ferromagnetic ground state. We find, however, a ferromagnetic ground state as expected on physical grounds. Our results exemplify the difficulties of the current DFT approaches to describe the magnetic properties of transition metal systems.

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Many-Body Effects in FeN4 Center Embedded in Graphene

Applied Sciences ◽

10.3390/app10072542 ◽

2020 ◽

Vol 10 (7) ◽

pp. 2542 ◽

Cited By ~ 1

Author(s):

Andrew Allerdt ◽

Hasnain Hafiz ◽

Bernardo Barbiellini ◽

Arun Bansil ◽

Adrian E. Feiguin

Keyword(s):

Transition Metal Complexes ◽

First Principles ◽

Density Functional ◽

Coulomb Repulsion ◽

Density Matrix Renormalization Group ◽

Orbital Interaction ◽

Many Body ◽

Generalized Gradient ◽

Functional Theory ◽

Density Matrix Renormalization

We introduce a computational approach to study porphyrin-like transition metal complexes, bridging density functional theory and exact many-body techniques, such as the density matrix renormalization group (DMRG). We first derive a multi-orbital Anderson impurity Hamiltonian starting from first principles considerations that qualitatively reproduce generalized gradient approximation (GGA)+U results when ignoring inter-orbital Coulomb repulsion U ′ and Hund exchange J. An exact canonical transformation is used to reduce the dimensionality of the problem and make it amenable to DMRG calculations, including all many-body terms (both intra- and inter-orbital), which are treated in a numerically exact way. We apply this technique to FeN 4 centers in graphene and show that the inclusion of these terms has dramatic effects: as the iron orbitals become single occupied due to the Coulomb repulsion, the inter-orbital interaction further reduces the occupation, yielding a non-monotonic behavior of the magnetic moment as a function of the interactions, with maximum polarization only in a small window at intermediate values of the parameters. Furthermore, U ′ changes the relative position of the peaks in the density of states, particularly on the iron d z 2 orbital, which is expected to affect the binding of ligands greatly.

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A density functional study of Rh13

Canadian Journal of Chemistry ◽

10.1139/cjc-2012-0493 ◽

2013 ◽

Vol 91 (7) ◽

pp. 591-597 ◽

Cited By ~ 11

Author(s):

Patrizia Calaminici ◽

José M. Vásquez-Pérez ◽

Diego A. Espíndola Velasco

Keyword(s):

Molecular Dynamics ◽

Ground State ◽

Density Functional ◽

Local Density ◽

Structural Parameters ◽

Functional Study ◽

Ground State Structure ◽

State Structure ◽

Generalized Gradient ◽

Density Functional Study

A density functional study was performed for the Rh13 cluster using the linear combination of Gaussian-type orbitals density functional theory (LCGTO-DFT) approach. The calculations employed both the local density approximation (LDA) as well as the generalized gradient approximation (GGA) in combination with a quasi-relativistic effective core potential (QECP). Initial structures for the geometry optimization were taken along Born–Oppenheimer molecular dynamics (BOMD) trajectories. The BOMD trajectories were performed at different temperatures and considered different potential energy surfaces (PES). As a result, several hundred isomers of the Rh13 cluster in different spin multiplicities were optimized with the aim to determine the lowest energy structures. All geometry optimizations were performed without any symmetry restriction. A vibrational analysis was performed to characterize these isomers. Structural parameters, relative stability energy, harmonic frequencies, binding energy, and most relevant Kohn–Sham (KS) molecular orbitals are reported. The obtained results are compared with available data from the literature. This study predicts a low symmetry biplanarlike structure as the ground-state structure of Rh13 with 11 unpaired electrons. This isomer was first noticed by inspection of first-principle Born–Oppenheimer molecular dynamics (BOMD) simulations between 300 and 600 K. This represents the most extensive theoretical study on the ground-state structure of the Rh13 cluster and underlines the importance of BOMD simulations to fully explore the PES landscapes of complicated systems.

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Energetics and electronic structures of perylene confined in carbon nanotubes

Royal Society Open Science ◽

10.1098/rsos.180359 ◽

2018 ◽

Vol 5 (6) ◽

pp. 180359 ◽

Cited By ~ 1

Author(s):

Yuya Nagasawa ◽

Takeshi Koyama ◽

Susumu Okada

Keyword(s):

Carbon Nanotubes ◽

Density Functional Theory ◽

Ground State ◽

Electronic Structures ◽

Density Functional ◽

Molecular Conformation ◽

Generalized Gradient ◽

Functional Theory ◽

Molecular Conformations ◽

Generalized Gradient Approximation

The energetics and geometries of perylene encapsulated in carbon nanotubes (CNTs) have been investigated employing density functional theory using the generalized gradient approximation combined with the van der Waals correction. Our calculations show that the encapsulated perylene molecules possess two metastable molecular conformations with respect to the CNT wall, which are almost degenerate with each other. A standing conformation, with respect to the CNT wall, is the ground state conformation for a semiconducting (19,0)CNT, while a lying conformation is the ground state for a metallic (11,11)CNT. Cooperation and competition between perylene–perylene and perylene–CNT interactions cause these possible perylene conformations inside CNTs. However, the electronic structure of the CNT encapsulating the perylene molecules is found to be insensitive to the molecular conformation.

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Structures and stabilities of (OsnN)0,±(n = 7 − 11) clusters

International Journal of Modern Physics B ◽

10.1142/s0217979215501635 ◽

2015 ◽

Vol 29 (23) ◽

pp. 1550163

Author(s):

W. L. Guo ◽

L. L. Zhang ◽

M. Luo ◽

X. R. Zhang

Keyword(s):

Density Functional Theory ◽

Ionization Potential ◽

Electron Affinity ◽

Ground State ◽

Density Functional ◽

Magic Number ◽

Generalized Gradient ◽

Functional Theory ◽

Generalized Gradient Approximation ◽

Ground State Structures

Structures and stabilities of [Formula: see text] clusters have been systematically studied via using density functional theory (DFT) with generalized gradient approximation (GGA). The calculations show that the stable configurations of [Formula: see text] are such structures with one N atom bonded to the external of the basic constructions consisting of Os atoms. Meanwhile, [Formula: see text] clusters [Formula: see text] represent “magic number” effect, and 8 is the magic number. Additionally, the ground-state structures of [Formula: see text] clusters have the best stability, while that of [Formula: see text] cluster possesses the worst stability. The result of the study on the ionization potential (IP) and the electron affinity (EA) shows that there are not topological differences among the configurations of [Formula: see text][Formula: see text] clusters.

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Density Functional Calculation of Property of the (1 0 0) Surface of γ-Pu

18th International Conference on Nuclear Engineering: Volume 3 ◽

10.1115/icone18-29071 ◽

2010 ◽

Author(s):

Rusong Li ◽

Bin He ◽

Quanhu Zhang ◽

Qianwei Du

Keyword(s):

Fermi Level ◽

Density Functional ◽

Atomic Orbital ◽

Relativistic Effects ◽

Local Property ◽

Density Functional Calculation ◽

Generalized Gradient ◽

Functional Theory ◽

Surface Corrosion ◽

Generate Surface

Pu material can generate surface corrosion and self-radiation effect during storage, leading to the creation and recoil of uranium and helium ions, which produce defects through displacement cascades, these self-irradiation defects tend to change plutonium properties. To study these aging behavior, calculations at the spin unrestricted generalized gradient approximation (GGA) level of density functional theory (DFT) have been performed using the DMol3 programs. Relativistic effects, such as mass-velocity, Darwin term, are considered in this code. Some conclusions are draw as follows: 1) Band structure of the (100) surface of γ-Pu is very narrow around the Fermi level, showing that the eigenstate of this level is mainly composed of local atomic orbital, the local property of electrons in this band is very strong, while the band around the Fermi level is mainly constituted by 5f narrow band; 2) DOS of the (100) surface of γ-Pu are mainly composed of the density of states in −48–41eV, −23–16eV, −3–2eV; 3) Contribution of s shell to the total DOS is mainly distributed in the first interval, and p shell is mainly in the second interval, while d and f shells are mainly in the third interval.

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FIRST-PRINCIPLES STUDY OF MAGNETISM AND DEFECT STATE PROPERTIES OF ANTIPEROVSKITE GaC1-xMn3

Modern Physics Letters B ◽

10.1142/s0217984910023001 ◽

2010 ◽

Vol 24 (10) ◽

pp. 953-962 ◽

Cited By ~ 2

Author(s):

L. HUA ◽

L. WANG ◽

L. F. CHEN

Keyword(s):

Ground State ◽

First Principles ◽

Density Functional ◽

Unit Cell Volume ◽

Magnetic Transition ◽

Generalized Gradient ◽

Functional Theory ◽

Generalized Gradient Approximation ◽

Spin Polarized ◽

Volume Decrease

We have investigated the electronic and magnetic properties of GaC 1-x Mn 3 (x = 0, 0.125, 0.25) using first-principles density functional theory within the generalized gradient approximation (GGA) + U schemes. The crystal structures of the compounds are cubic for x = 0, 0.125, 0.25. The lattice parameters and unit cell volume decrease as the C vacancy increase. Our spin polarized calculations give metallic ground state for x = 0, 0.125, 0.25. The magnetic structure for x = 0, 0.125 are antiferromagnetic, while for x = 0.25 it is ferromagnetic. From the density of states (DOS), the hybridization between the C 2p and Mn 3d state is the main reason for magnetic transition.

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Density Functional Study of the Structural Properties of Copper Iodide: LDA vs GGA Calculations

Journal of Nano Research ◽

10.4028/www.scientific.net/jnanor.5.25 ◽

2009 ◽

Vol 5 ◽

pp. 25-30 ◽

Cited By ~ 8

Author(s):

Heribert Hernández-Cocoletzi ◽

Gregorio H. Cocoletzi ◽

J.F. Rivas-Silva ◽

A. Flores ◽

Noboru Takeuchi

Keyword(s):

Structural Properties ◽

Ground State ◽

Density Functional ◽

Local Density ◽

Structural Parameters ◽

External Pressure ◽

Functional Study ◽

Full Potential ◽

Copper Iodide ◽

Generalized Gradient

We have performed first principles total energy calculations to investigate the structural properties of copper iodide (CuI) in its sodium chloride, cesium chloride, zincblende and wurtzite structures. Calculations are done using the density functional theory. We employ the full potential linearized augmented plane wave method as implemented in the wien2k code. The exchange and correlation potential energies are treated in the generalized gradient approximation (GGA), and the local density approximation (LDA). Optical absorption experiments and x-ray diffraction measurements have shown that zincblende is the ground state of CuI. Our calculations find that in the GGA formalism wurtzite and zincblende have similar total energies, while in the LDA formalism the lowest minimum corresponds to zincblende. Results show that the energy difference between the wurtzite and the zincblende structures, as calculated within the GGA formalism is 2 meV, and within the LDA formalism, is 31 meV. These results may suggest a coexistence of both wurtzite and zincblende structures in the ground state of CuI. Structural parameters are correctly reproduced by the GGA calculations. We obtain that under the application of external pressure the atomic configuration may transform into the NaCl structure. At higher pressures it is possible to have a phase transition to the CsCl geometry.

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GGA + U and mBJ + U study of the optoelectronic, magnetic and thermoelectric properties of the SmAlO3 compound with spin–orbit coupling

International Journal of Modern Physics B ◽

10.1142/s0217979216500788 ◽

2016 ◽

Vol 30 (12) ◽

pp. 1650078 ◽

Cited By ~ 10

Author(s):

Sandeep Chettri ◽

D. P. Rai ◽

A. Shankar ◽

R. Khenata ◽

M. P. Ghimire ◽

...

Keyword(s):

Thermoelectric Properties ◽

Electronic Structures ◽

Density Functional ◽

Orbit Coupling ◽

Full Potential ◽

Potential Candidate ◽

Spin Orbit Coupling ◽

Spin Orbit ◽

Thermoelectric Efficiency ◽

Generalized Gradient

The electronic, thermoelectric, optical, and magnetic properties of the samarium aluminate (SmAlO3) compound is studied using the spin-polarized full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). The exchange and correlation potential is treated with the generalized gradient approximation (GGA) and the Coulomb repulsion ([Formula: see text] Ry) has been calculated theoretically and was used for the GGA[Formula: see text] based approximated electronic structures. Additionally, the modified Becke–Johnson (mBJ) potential was also utilized along with the GGA[Formula: see text] approach for the calculation of the band gap. On the other hand, the optical properties were analyzed with the mBJ[Formula: see text] results and the thermoelectric properties were explained on the basis of the electronic structures and density of states (DOS) with a thermoelectric efficiency of 0.66 at 300 K. The minimum reflectivity at 1.13 eV (which was equal to 1.097 [Formula: see text]m) was found to be in agreement with the experimental results. Further refinements in the electronic structures were obtained by adding the spin–orbit coupling (SOC) interactions to the GGA[Formula: see text] approach, which was then combined with the mBJ approximations. Hence, a conclusion using the combined mBJ[Formula: see text]SOC study indicates that the SmAlO3 compound is a potential candidate for both thermoelectric as well as magnetic devices.

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