We investigate the electronic structure of molecules and solids with theoretical
methods based on Quantum Mechanics, to interpret or predict their physical and
chemical properties, such as: structural properties (interatomic distances,
angles, etc), energies and probabilities of electronic transitions, ionization
energies, charges, photoelectron spectra, magnetic properties (magnetic moments,
magnetic coupling constant J), magnetic hyperfine properties (hyperfine fields,
EPR A tensor), Mössbauer hyperfine parameters (isomer shifts, electric-field
gradients), etc.
RESEARCHERS
Diana
Guenzburger (Professor)
Joice Terra (Professor)
Javier Antonio Gómez Romero (graduate student)
Patrícia Granzotto Antunes (graduate student)
Donald E. Ellis (visiting scholar from Northwestern University, U.S.A)
Zeng Zhi (visiting scholar from the Institute of Solid State, Hefei, R. P.
China)
THEORETICAL METHODS
For
the Quantum Mechanical calculations we employ the Discrete Variational method
(DVM) (D. E. Ellis and G. S. Painter, Phys. Rev. B 2, 2887 (1970), D. E. Ellis
and D. Guenzburger, Adv. Quant. Chem. 34, 51 (1999)), within Density Functional
theory (see also the site http://dvworld.nwu.edu).
DVM is an all-numerical method, with which we can obtain the electronic
structure of both molecules and solids. In the case of solids, the crystal is
represented by a group of up to 100-150 atoms (cluster) , embedded in the
potential of several thousands of atoms of the external solid. Since no
translational symmetry is necessary, solid systems without periodicity may be
treated, such as impurities, amorphous solids, defects, vacancies, etc.
In systems with heavy atoms, relativistic effects become important. For these we
employ the four-component relativistic version of DVM, with which the
Coulomb-Dirac equation is solved in the framework of Density Functional theory.
For very complex systems, it is not possible to calculate structural parameters
with Quantum Mechanical methods. For these cases, we employ the tools of
Molecular Dynamics, in which the interactions are treated classically. Coupled
to DVM, this procedure gives interatomic distances and equilibrium values of the
angles (K. C. Mundim and D. E. Ellis, Braz. J. Phys. 29, 199 (1999)).
RESEARCH
INTERESTS
Molecular Orbital methods for molecules and clusters. Hartree-Fock,
semi-empirical methods, Density Functional theory.
Optical and photoelectron spectroscopy studied with Quantum Mechanical methods.
Mössbauer hyperfine interactions and their relation to electronic structure.
Transition metal complexes: chemical bonding, optical spectra, ionization
energies, Mössbauer hyperfine interactions, EPR hyperfine parameters.
Metals, alloys, intermetallic compounds and small metal particles: electronic
structure, magnetic properties, hyperfine interactions.
Electronic structure and related properties of ionic crystals and
semiconductors.
Relativistic electronic structure calculations for atoms, molecules and solids.
Localized magnetism in metals, dilute alloys and metallic precipitates.
Electronic structure, hyperfine properties and magnetism in superconductors.
Nanoscopic magnetic systems; transition metal molecules of nanoscale dimensions.
Magnetism and hyperfine interactions.
Relativistic calculations for Rare Earth compounds.
Electronic structure of interfaces and monolayers: metal/metal,
metal/semiconductor, semiconductor/semiconductor.
Electronic structure of large biological molecules containing transition
elements: electronic, magnetic and hyperfine properties.
Electronic structure of silicates and zeolites.
Electronic structure of Hydroxyapatite, with and without substitutional
impurities.
CURRENT
PROJECTS
A
molécula Myoglobin is a biological molecule present in muscle and containing
Fe. We are investigating its electronic structure and the interaction with the
ligand NO. We are calculating the hyperfine parameters at the N atoms, to help
in the interpretation of EPR and ENDOR spectra.
Extensive calculations were performed for embedded clusters representing 3, 4
and 5 monolayers of Fe on fcc Cu(001) . Several magnetic configurations were
considered. We obtained hyperfine fields, magnetic moments and electric-field
gradients. Currently, the calculations are being extended to monolayers of Co
on Cu(001).
Four-component relativistic calculations are being performed for the layered
compounds EuCo2P2 , EuRh2P2 and EuRh2As2 . We are investigating the effect of
pressure on the magnetic properties and on the Mössbauer isomer shifts.
Zeolites have a three dimensional framework arising from open AlO4 tetrahedra
linked by one oxygen. The resulting system of channels allows these materials
to efficiently function as molecular sieves, as well as to act as ion
exchangers, adsorbents and catalysts. Zeolites have applications in a wide
variety of fields, including bulk separation processes, gasoline refinement,
and long-term storage of nuclear waste products. In this project we are
studying a new family of zeolites based on ALPO4: the aluminophosphates. We are
interested in electronic properties and in the adsorption of organic molecules
such as methanol. We employ a computational scheme based on classical Molecular
Dynamics (MD), Monte Carlo (MC/GSA) stochastic sampling, and Density Functional
quantum mechanics procedures (SCF-DV) coupled together.
Layered silicates of T-O-T structure (mica group) are materials of great
scientific interest ( structures rich in Fe are fundamental to understand the
magnetic properties of minerals), and technological ( for instance , phlogopite
mica was used as cesium ion sieve in the decontamination of the environment
with radioactive 137Cs in the Chernobyl nuclear reactor accident - Science
239(1988)1286)). Our interest in micas, particularly annite, is related to the
hyperfine interactions as measured by Mössbauer spectroscopy. Currently we are
investigating the magnetic order of annite by calculating the Heisenberg
exchange constant: mica is a natural laboratory to study 2D magnetism.
Bioceramic materials in general, and hydroxyapatite in particular are of
enormous interest in biological and medical sciences. Hydroxyapatite (HAP) is
the basic minearal component of hard tissues ( bones, dental enamel, etc ).
However, HAP is not only important as a bioceramic. Due to its cation-exchange
property, it can be used for treatment or confinement of industrial or nuclear
wastes, as well as the implantation of metal ions forming catalytically active
materials. Although HAP is the subject of extensive experimental studies,
theoretical investigations are still limited. In this project we are
investigating, by using density functional theory and atomistic simulations,
the substitution of cationic and anionic sites in HAP by metals ( such as Fe,
Co, Cu, Zn, Cd, Hg, e Pb ) , and the carbonated radicals CO2 , CO3 . Our
results are compared with experimental data from EPR, ENDOR, Mössbauer
spectroscopy and XANES, among others.
PUBLICATIONS SINCE 1995
1.
"Electric-field gradients and magnetic hyperfine parameters of
square-pyramidal [M(CN)5]3- (M = Co, Rh and Ir) complexes".
S.R.Nogueira e D.Guenzburger.
Int. J. Quantum Chem. 54, 381-392 (1995).
2.
"Theoretical study of the pyramidal geometry around the sulfur in the
S-bound mode of coordination of thiophene to the [CP(CO)2Fe]+ fragment".
L.Rincón, J.Terra, D.Guenzburger e R.Sanchez-Delgado.
Organometallics 14, 1292-1296 (1995).
3.
"Density Functional study of Fe bound to ammonia".
Joice Terra e Diana Guenzburger
Journal of Physical Chemistry 99, 4935-4940 (1995).
4.
"Magnetic and hyperfine properties of fcc Fe".
Diana Guenzburger e D.E.Ellis.
Physical Review B 51, 12.519-12.522 (1995).
5.
"Magnetic and electronic properties of g-Fe and g-Fe/Al particles in
copper".
Diana Guenzburger e D.E.Ellis.
Physical Review B 52, 13 390-13 398 (1995)
6.
"Relativistic effects on the electronic structure and bonding of
[Ir(CN)5]3-".
S.R.Nogueira e D.Guenzburger.
Int. Journal of Quantum Chemistry 57 , 471-479 (1996)
7.
"Electronic structure of Ni substituted Y(Ni1-xMx)2B2C
superconductors".
Z.Zeng, D.E.Ellis, Diana Guenzburger e E.M.B.Saitovitch.
Physical Review B 53, 6613-6621 (1996)
8.
"Density functional study of fcc iron and iron particles in copper"
Diana Guenzburger e D.E.Ellis
J. Applied Physics 8, 6429-6431 (1996)
9.
"Spin density and magnetism of rare-earth nickel borocarbides:
RENi2B2C"
Z.Zeng,D.E.Ellis, Diana Guenzburger e E.M.Baggio-Saitovitch,
Physical Review B 54, 13020-13029 (1996)
10.
"Effect of magnetism on superconductivity in rare-earth compounds
RENi2B2C"
Z.Zeng, Diana Guenzburger, D.E.Ellis e E.M.B.Saitovitch
Physica C 271 , 23-31 (1996).
11.
"Hyperfine Interaction in Layered Silicates"
Joice Terra e D. E. Ellis
Hyperfine Interactions 2, 82-88 (1997).
12.
"Electronic Structure, Chemical Bonding and Hyperfine Parameters in Layered
Silicates"
Joice Terra e D. E. Ellis
Physical Review B 56, 1834-1847 (1997).
13.
"Mössbauer Spectroscopy of 57Fe in the compounds
RE(Ni0.99Fe0.01)2B2C(RE=Y, Gd, Tb, Dy, Ho, Er): Theory and experiment"
Z.Zeng, D.R.Sanchez, Diana Guenzburger, D.E.Ellis, E.M.Baggio-Saitovitch e H.
Micklitz,
Physical Review B 55, 3087-3092 (1997)
14.
"Electronic structure and hyperfine properties of molecules and solids by
cluster methods"
Diana Guenzburger
Proceedings da conferência Internacional Cray-UNAM "Computational
Chemistry", "Computational Chemistry and Chemical Engineering:
Proceedings of the third Cray- UNAM supercomputing Conference", editores
G.Cisneros, J.A.Cogordan, M.Castro e C.Wang, World Scientific, Singapore (1997),
pag. 149-158.
15.
"Magnetism, chemical bonding and hyperfine properties in the nanoscale
antiferromagnet [Fe(OMe)2 (O2 CCH2Cl)]10 "
Z. Zeng, Y. Duan e Diana Guenzburger, Physical Review B 55, 12522-12528 (1997).
16.
"Chemical bonding and Mössbauer hyperfine interactions"
Diana Guenzburger
Capítulo do livro em homenagem a Jacques Danon, editado por R. Scorzelli, I.
Souza Azevedo e E. Baggio-Saitovitch, "Essays on Interdisciplinary Topics
in Natural Sciences",
Editions Frontières, Paris (1997).
17.
"Spin and magnetism of Rare Earth-Nickel borocarbides :RENi2B2C"
Z Zeng, Diana Guenzburger, D. E. Ellis e E. M. B. Saitovitch, Physica C 282-287,
1633-1634 (1997).
18.
"First-principles calculations of Mössbauer hyperfine parameters for
solids and large molecules",
Diana Guenzburger, D. E. Ellis e Z. Zeng,
Hyperfine Interactions 113, 25-36 (1998).
19.
"Hyperfine Interactions of cis and trans Octahedral Fe2+ sites in the
Layered Silicate Annite"
Joice Terra e D. E. Ellis
Journal of the American Ceramic Society 8, 465 - 468 (1998).
20.
D. Guenzburger and Z. Zeng, "Electronic structure, magnetic and hyperfine
properties in nanoscale transition-metal clusters",
Proceedings of the 9th International Conference on Modern Materials and
Technologies,
Florence, Italy (1998).
21.
"The Discrete Variational method in Density Functional theory and its
applications to large molecules and solid-state systems"
D. E. Ellis e Diana Guenzburger
Advances in Quantum Chemistry 34, 51-141 (1999)
22.
"Electronic structure, spin coupling and hyperfine properties of nanoscale
molecular magnets",
Z. Zeng, Diana Guenzburger e D. E. Ellis,
Physical Review B 59, 6927-6937 (1999)
23.
"Density Functional study of electronic, magnetic and hyperfine properties
of [M(CN)5NO]2- (M=Fe, Ru) and reduction products"
J. A. Gómez e Diana Guenzburger
Chemical Physics 253, 73-89 (2000)
24.
"First-principles calculations of magnetic and hyperfine properties of
Fe/Cu(001) multilayers"
J. A. Gómez e Diana Guenzburger
accepted for publication in J. Mag. Magn. Materials (Proceedings ICM2000)
25.
"Fully relativistic calculations of the effect of pressure on the magnetism
of EuCo2P2"
Diana Guenzburger, D. E. Ellis e J. A. Gómez
accepted for publication in J. Mag. Magn. Materials (Proceedings ICM2000)
26.
"Influence of conduction electrons on the magnetism of cobalt grains in a
copper matrix studied by density-functional theory" ,
J. A. Gómez e Diana Guenzburger,
Physical Review B 63, 134404-1 - 134404-10 (2001)
27.
" Configuration of CO2- radicals in g- irradiated A - type carbonated
apatites: Theory and Experimental EPR and ENDOR studies"
Delson U. Schramm, Joice Terra, Alexandre M. Rossi, e D. E. Ellis
Physical Review B 63 , 024107-1 - 024107-14 (2001)
28.
" Characterization of Electronic Structure and Bonding in Hydroxiapatite:
Zn Substitution for Ca "
Joice Terra, Ming Jiang, e D. E. Ellis
Submetido para publicação.
29.
"Electronic, magnetic and hyperfine properties of fcc Fe monolayers on
Cu(001)",
J. A. Gómez e Diana Guenzburger
Submitted for publication
30.
"A relativistic one-electron approach to the effect of pressure on the
magnetism of EuCo2P2"
Diana Guenzburger, D. E. Ellis e J. A. Gómez
Submitted for publication.
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