Peter Fedders - Academia.edu (original) (raw)
Papers by Peter Fedders
Physical Review Letters, 1987
Physical Review Letters, 1974
A nonresonant mechanism, magnetization directional softness, is proposed to explain anomalous res... more A nonresonant mechanism, magnetization directional softness, is proposed to explain anomalous resonancelike ultrasonic absorption effects which have been observed in ferromagnetic metals by the present and by previous investigators. Magnetoelastic dispersion data are presented which provide independent evidence for this nonresonant mechanism. We assert that neither the present nor previous ultrasonic absorption measurements in bulk metals correspond to acoustic ferromagnetic resonance.
Hydrogen dimers can be found in Si as H2 and H2 . Although the energies of these two defect cente... more Hydrogen dimers can be found in Si as H2 and H2 . Although the energies of these two defect centers have been predicted to be within a few tenths of an eV of each other, the two dimers have never been seen simutaneously in a sample. Irradiation induces the conversion of H2 into H2 ^*. Our ab-intio molecular-dynamics simulations show in real-time the dissociation of H2 by intrinsic decfects and the conversion of H2 into H2 ^*.
Physical Review Letters, 1971
Physical Review B Condensed Matter, 1990
A new type of total-energy functional for semiconductors is proposed, using a form based on an ap... more A new type of total-energy functional for semiconductors is proposed, using a form based on an approximate quantum-mecahnical analysis. Two new types of terms are included: pair terms giving a matrix description of an atom's local environment, and cluster terms describing the ring topology. The scheme reproduces both the covalent and metallic behavior of semiconductor materials in the appropriate limits. A parametrized form of the scheme is applied to Si.
Physical Review B Condensed Matter and Materials Physics, Jun 21, 2002
A structural model of hydrogenated amorphous silicon containing an isolated dangling bond is used... more A structural model of hydrogenated amorphous silicon containing an isolated dangling bond is used to investigate the effects of electron interactions on the electronic level splittings, localization of charge and spin, and fluctuations in charge and spin. These properties are calculated with a recently developed density-matrix correlation-energy functional applied to a generalized Anderson Hamiltonian, consisting of tight-binding one-electron terms parametrizing hydrogenated amorphous silicon plus a local interaction term. The energy level splittings approach an asymptotic value for large values of the electron-interaction parameter U, and for physically relevant values of U are in the range 0.3-0.5 eV. The electron spin is highly localized on the central orbital of the dangling bond while the charge is spread over a larger region surrounding the dangling bond site. These results are consistent with known experimental data and previous density-functional calculations. The spin fluctuations are quite different from those obtained with unrestricted Hartree-Fock theory.
Phys Rev B, 1985
The information-theoretic maximum-entropy approach is used to obtain high-temperature dynamical s... more The information-theoretic maximum-entropy approach is used to obtain high-temperature dynamical spin-correlation functions from a finite number of rigorously known moments. The method is applied to the dipolar-broadened magnetic-resonance line-shape function for a simple cubic lattice and other spin-correlation functions. The results improve on the best previous theoretical results and agree with experiment to within ~2%. Modeling of the self-energy with the maximum-entropy method provides better results than direct modeling of the line-shape function. The results display an oscillating pattern of convergence which is expected to occur in many physical applications.
Physical review. B, Condensed matter, Jan 15, 1989
Physical review. B, Condensed matter, Jan 15, 1986
Physical review. B, Condensed matter, Jan 15, 1987
... " The Newman-Dow approach used two different types of long range appr-oximations: mean-f... more ... " The Newman-Dow approach used two different types of long range appr-oximations: mean-field theory (MFT), which does not include correlations, and the virtual-crystal approximation (VCA), which assumes that cluster statistics are unimportant. ...
![Research paper thumbnail of Publisher’s Note: Vacancy ordering phase transition in ZrBe2(H/D)x: NMR and electronic structure study [Phys. Rev. B 67, 045107 (2003)]](https://attachments.academia-assets.com/43624483/thumbnails/1.jpg)
](Physical Review B, 2003
The layered intermetallic compound ZrBe 2 ͑H/D͒ x (xӍ1.5) was studied using deuterium and berylli... more The layered intermetallic compound ZrBe 2 ͑H/D͒ x (xӍ1.5) was studied using deuterium and beryllium NMR. A temperature-induced structural transition in the deuteride reported earlier is further investigated here using 9 Be NMR, which reveals the transition in both the hydride and deuteride at 200 and 235 K, respectively. Above the transition temperature a single pair of quadrupolar satellites is present. Each quadrupolar satellite splits into two resonances below the transition temperature, implying the existence of two different classes of Be sites. The temperature dependence of the satellite frequencies and the appearance of two-phase coexistence spectra show the transition to be first order. Be-D spin-echo double resonance ͑SEDOR͒ experiments were performed to identify the two sites; SEDOR demonstrates that the D environments of the two classes of Be sites are similar. Electronic structure calculations show the binding energy of H decreases gradually for x greater than 1.38. The calculations allow a vacancy ordered structure to be proposed.
Physical Review Letters, 1987
Physical Review Letters, 1974
A nonresonant mechanism, magnetization directional softness, is proposed to explain anomalous res... more A nonresonant mechanism, magnetization directional softness, is proposed to explain anomalous resonancelike ultrasonic absorption effects which have been observed in ferromagnetic metals by the present and by previous investigators. Magnetoelastic dispersion data are presented which provide independent evidence for this nonresonant mechanism. We assert that neither the present nor previous ultrasonic absorption measurements in bulk metals correspond to acoustic ferromagnetic resonance.
Hydrogen dimers can be found in Si as H2 and H2 . Although the energies of these two defect cente... more Hydrogen dimers can be found in Si as H2 and H2 . Although the energies of these two defect centers have been predicted to be within a few tenths of an eV of each other, the two dimers have never been seen simutaneously in a sample. Irradiation induces the conversion of H2 into H2 ^*. Our ab-intio molecular-dynamics simulations show in real-time the dissociation of H2 by intrinsic decfects and the conversion of H2 into H2 ^*.
Physical Review Letters, 1971
Physical Review B Condensed Matter, 1990
A new type of total-energy functional for semiconductors is proposed, using a form based on an ap... more A new type of total-energy functional for semiconductors is proposed, using a form based on an approximate quantum-mecahnical analysis. Two new types of terms are included: pair terms giving a matrix description of an atom's local environment, and cluster terms describing the ring topology. The scheme reproduces both the covalent and metallic behavior of semiconductor materials in the appropriate limits. A parametrized form of the scheme is applied to Si.
Physical Review B Condensed Matter and Materials Physics, Jun 21, 2002
A structural model of hydrogenated amorphous silicon containing an isolated dangling bond is used... more A structural model of hydrogenated amorphous silicon containing an isolated dangling bond is used to investigate the effects of electron interactions on the electronic level splittings, localization of charge and spin, and fluctuations in charge and spin. These properties are calculated with a recently developed density-matrix correlation-energy functional applied to a generalized Anderson Hamiltonian, consisting of tight-binding one-electron terms parametrizing hydrogenated amorphous silicon plus a local interaction term. The energy level splittings approach an asymptotic value for large values of the electron-interaction parameter U, and for physically relevant values of U are in the range 0.3-0.5 eV. The electron spin is highly localized on the central orbital of the dangling bond while the charge is spread over a larger region surrounding the dangling bond site. These results are consistent with known experimental data and previous density-functional calculations. The spin fluctuations are quite different from those obtained with unrestricted Hartree-Fock theory.
Phys Rev B, 1985
The information-theoretic maximum-entropy approach is used to obtain high-temperature dynamical s... more The information-theoretic maximum-entropy approach is used to obtain high-temperature dynamical spin-correlation functions from a finite number of rigorously known moments. The method is applied to the dipolar-broadened magnetic-resonance line-shape function for a simple cubic lattice and other spin-correlation functions. The results improve on the best previous theoretical results and agree with experiment to within ~2%. Modeling of the self-energy with the maximum-entropy method provides better results than direct modeling of the line-shape function. The results display an oscillating pattern of convergence which is expected to occur in many physical applications.
Physical review. B, Condensed matter, Jan 15, 1989
Physical review. B, Condensed matter, Jan 15, 1986
Physical review. B, Condensed matter, Jan 15, 1987
... " The Newman-Dow approach used two different types of long range appr-oximations: mean-f... more ... " The Newman-Dow approach used two different types of long range appr-oximations: mean-field theory (MFT), which does not include correlations, and the virtual-crystal approximation (VCA), which assumes that cluster statistics are unimportant. ...
Physical Review B, 2003
The layered intermetallic compound ZrBe 2 ͑H/D͒ x (xӍ1.5) was studied using deuterium and berylli... more The layered intermetallic compound ZrBe 2 ͑H/D͒ x (xӍ1.5) was studied using deuterium and beryllium NMR. A temperature-induced structural transition in the deuteride reported earlier is further investigated here using 9 Be NMR, which reveals the transition in both the hydride and deuteride at 200 and 235 K, respectively. Above the transition temperature a single pair of quadrupolar satellites is present. Each quadrupolar satellite splits into two resonances below the transition temperature, implying the existence of two different classes of Be sites. The temperature dependence of the satellite frequencies and the appearance of two-phase coexistence spectra show the transition to be first order. Be-D spin-echo double resonance ͑SEDOR͒ experiments were performed to identify the two sites; SEDOR demonstrates that the D environments of the two classes of Be sites are similar. Electronic structure calculations show the binding energy of H decreases gradually for x greater than 1.38. The calculations allow a vacancy ordered structure to be proposed.