Showing papers on "Ground state published in 1975"
TL;DR: In this paper, a new theory of spin glasses is proposed, which offers a simple explanation of the cusp found experimentally in the susceptibility, which is smoothed by an external field.
Abstract: A new theory of the class of dilute magnetic alloys, called the spin glasses, is proposed which offers a simple explanation of the cusp found experimentally in the susceptibility. The argument is that because the interaction between the spins dissolved in the matrix oscillates in sign according to distance, there will be no mean ferro- or antiferromagnetism, but there will be a ground state with the spins aligned in definite directions, even if these directions appear to be at random. At the critical temperature the existence of these preferred directions affects the orientation of the spins, leading to a cusp in the susceptibility. This cusp is smoothed by an external field. Although the behaviour at low t needs a quantum mechanical treatment, it is interesting to complete the classical calculations down to t=0. Classically the susceptibility tends to a constant value at t=0, and the specific heat to a constant value.
2,965 citations
TL;DR: A survey of the electron affinity determinations for the elements up to Z=85 is presented, and based upon these data, a set of recommended electron affinities is established.
Abstract: This article updates a ten‐year‐old review of this subject [J. Chem. Phys. Ref. Data 4, 539 (1975)]. A survey of the electron affinity determinations for the elements up to Z=85 is presented, and based upon these data, a set of recommended electron affinities is established. Recent calculations of atomic electron affinities and the major semiempirical methods are discussed and compared with experiment. The experimental methods which yield electron binding energy data are described and intercompared. Fine structure splittings of these ions and excited state term energies are given.
1,297 citations
TL;DR: In this paper, the Hartree-Fock (UHF) Hamiltonian is used as the unperturbed system and the technique is described as unrestricted Mo-Plesset to second order (UMP2).
Abstract: Mo–Plesset theory, in which electron correlation energy is calculated by perturbation techniques, is used in second order to calculate energies of the ground states of atoms up to neon. The unrestricted Hartree–Fock (UHF) Hamiltonian is used as the unperturbed system and the technique is then described as unrestricted Mo–Plesset to second order (UMP2). Use of large Gaussian basis sets suggests that the limiting UMP2 energies with a complete basis of s, p, and d functions account for 75–84% of the correlation energy. Preliminary estimates of the contributions of basis functions with higher angular quantum numbers indicate that full UMP2 limits give even more accurate total energies.
782 citations
TL;DR: In this paper, the authors generalize Lai's model to higher-spin systems and a lattice of SU(3) triplets, making application to various systems such as dilute Heisenberg magnets.
Abstract: In a recent paper, Lai introduced a lattice-gas model. In this paper we generalize Lai's model, making application to various systems such as dilute Heisenberg magnets, higher-spin systems, and a lattice of SU(3) triplets. By a careful consideration of general thermodynamic stability, and by variational arguments, we demonstrate Lai's solution to be incorrect, and in turn produce the correct solution in this case and in other cases including higher-dimensional models. The remaining cases we treat in one dimension by Bethe's ansatz, reducing the problem to coupled integral equations. We locate the singularities of the ground-state energy in the phase plane; and we explicitly calculate the absolute-ground-state energy, excitations above the absolute ground state, and the first correction to the absolute ground state for small concentrations of impurities.
760 citations
642 citations
TL;DR: In this article, a doubly excited model atom with interactions between its two "electrons" having an infinite lifetime is presented. But the model is based on a deterministic model.
Abstract: Quantum-mechanical examples have been constructed of local potentials with bound eigenstates embedded in the dense continuum of scattering states. The method employed corrects and extends a procedure invented by von Neumann and Wigner. Cases are cited whereby deformation of the local potential causes the continuum bound state to move downward through the bottom of the continuum, and to connect analytically to a nodeless ground state. A doubly excited model atom is also displayed, with interactions between its two "electrons," having an infinite lifetime (in the Schr\"odinger equation regime). In the light of these examples, attention is focused on quantitative interpretation of real tunneling phenomena, and on the existence of continuum bound states in atoms and molecules.
574 citations
TL;DR: In this article, the fluorescence excitation spectrum of NO2 was measured in the region 5708-6708 A using a tuneable dye laser as an excitation source.
Abstract: The fluorescence excitation spectrum of NO2 was measured in the region 5708–6708 A using a tuneable dye laser as an excitation source. The NO2 was cooled to a rotational temperature of ∼3 K by expansion with argon as a carrier gas through a supersonic nozzle. This cooling drastically reduced the rotational structure and thereby permitted a clear separation and analysis of 140 vibronic bands found in this 1000 A region of the spectrum. The results indicate that most of the fluorescence in this region is due to a 2B2 electronic state, and that this state is so heavily perturbed by high lying levels of the ground electronic state that a substantial fraction of all ground state levels of appropriate vibronic symmetry in this region have appreciable fluorescence intensity.
294 citations
IBM1
TL;DR: In this article, Kohn and Sham showed that the cohesive energy, lattice constant, and bulk modulus of Li, Be, Na, Al, Ar, K, Ca, and Cu can be computed using the local density scheme of Kohn, to within \ensuremath{\sim}20% and \ensuresuremath{sim}03 Bohr radii, and ≤ 1.10% respectively, of experimental values.
Abstract: We show that the cohesive energy, lattice constant, and bulk modulus of Li, Be, Na, Al, Ar, K, Ca, and Cu can be calculated using the local-density scheme of Kohn and Sham, to within \ensuremath{\sim}20%, \ensuremath{\sim}03 Bohr radii, and \ensuremath{\sim}10%, respectively, of experimental values These calculations are truly a priori in that the only inputs are the atomic number $Z$ and the zero-point lattice properties Self-consistent crystal calculations were performed using the muffin-tin approximation, and atomic calculations were performed using the spin-polarized exchange-correlation functional constructed by von Barth and Hedin The results show that these approximations are adequate for computing the equilibrium properties of crystals (errors in the computed pressure-volume relations are less than \ensuremath{\sim} 10 kbar), but errors occur in the atomic calculations for atoms with more than one electron outside a closed shell, and possibly in the muffin-tin approximation for transition-element crystals
272 citations
TL;DR: In this article, a multiconfiguration self-consistent field (MC-SCF) wavefunctions have been computed for the low-lying X 2A1, A 2B2, B 2B1, C 2A2, 4B2 and 2Σ+g electronic states of NO2.
Abstract: Traditional spectroscopic analysis of the complex and irregular absorption spectrum of NO2 has provided a relatively small amount of information concerning the nature of the excited states. An extensive ab initio investigation has been undertaken, therefore, to provide a basis for interpretation of the experimental results. Multiconfiguration self‐consistent‐field (MC–SCF) wavefunctions have been computed for the low‐lying X 2A1, A 2B2, B 2B1, C 2A2, 4B2, 4A2, and 2Σ+g electronic states of NO2. The minima of the A 2B2, B 2B1, and C 2A2 states have all been found to be within 2 eV of the minimum of the X 2A1 ground state; for these states, C2v potential surfaces have been constructed for purposes of a spectral interpretation. The 4B2, 4A2, and 2Σ+g states are all more than 4 eV above the minimum of the ground state and have been examined in less detail. The study described here significantly improves on previous NO2 ab initio calculations in three important areas: (1) The double‐zeta‐plus‐polarization quality basis set is larger and more flexible; (2) the treatment of molecular correlation is more extensive; and (3) the electronic energies have been calculated for several different bond lengths and bond angles in each state. For the four lowest doublet states the following spectral data have been obtained: The ground state experimental constants are included in parentheses. The estimated accuracy of the various parameters is ±0.02 A for bond length, ±2° for bond angle, ±10% for the vibrational frequencies, ±0.10 D for dipole moments, and ±0.3 eV for the adiabatic excitation energies. An unusual feature has been found for the 2Σ+g state. The equilibrium geometry of this linear state has two unequal bond lengths of 1.20 A and 1.42 A and the inversion barrier is approximately 800 cm−1.
253 citations
TL;DR: In this article, a particle hole-interaction has been derived which gives a good account of the non-normal parity states of a number of nuclei from 11Be to 16O.
248 citations
TL;DR: In this paper, the R-matrix method was used to calculate electron-atom and ion collision cross sections and atomic polarizabilities to enable atomic photoionization processes to be studied.
Abstract: The R-matrix method, which has been used recently to calculate electron-atom and ion collision cross sections and atomic polarizabilities is extended to enable atomic photoionization processes to be studied. Both the initial atomic bound state and the final atomic continuum state are expanded in terms of R-matrix bases. The method is programmed for a general atomic system and then used to calculate the photoionization cross sections of ground state neon and argon atoms leaving the residual ions in their ground or first excited states. Good agreement is obtained with recent experiments using synchrotron radiation both in resonant and non-resonant regions, showing that the method has a wide range of applicability.
TL;DR: In this article, the results of extensive configuration interaction calculations (double ζ basis) on the ground and 15 excited states of ozone and the eight lowest states of the ozone positive ion are carried out as a function of both bond length and bond angle.
Abstract: We report the results of extensive configuration interaction calculations (double ζ basis) on the ground and 15 excited states of ozone and the eight lowest states of the ozone positive ion. The studies on ozone are carried out as a function of both bond length and bond angle. We find that three excited states of ozone may be bound with respect to the ground states of O2 and O. Additional information is provided on the ring state (60 ° bond angle) previously reported. Two of the excited states of ozone are known spectroscopically and the ionization potentials of the first three states of O+3 are now known experimentally. These experimental results are in good agreement with the theoretical calculations.
TL;DR: In this article, a theoretical analysis of spontaneous emission from an excited atom or a molecule in a one-dimensional periodic structure formed by a screened two-conductor line filled with periodically distributed dielectric disks is made.
Abstract: A theoretical analysis is made of the spontaneous emission from an excited atom or a molecule in a one-dimensional periodic structure formed by a screened two-conductor line filled with periodically distributed dielectric disks. It is shown that when the transition frequency lies within or close to the forbidden band of the periodic structure, the decay of an excited state of an atom or a molecule produces a characteristic long-lived dynamic state. This dynamic state is a superposition of the excited and ground states with an admixture of a photon "cloud," which surrounds the atom or molecule. A study is made of the distribution of the electromagnetic energy of the dynamic state. The energy and the decay law of the excited state are obtained and the spectrum of the emission which accompanies this decay is obtained. It is shown that the spontaneous emission can be suppressed strongly in volumes much greater than the wavelength. The possibility of the suppression of spontaneous emission from lasers is discussed.
TL;DR: In this paper, the vibronic structure of the first singlet π→π* transition of cis− and trans−stilbene is calculated as a step in the detailed study of photoisomerization reactions.
Abstract: The calculations of the vibronic structure of the first singlet π→π* transition of cis− and trans−stilbene are presented as a step in the detailed study of photoisomerization reactions. In order to obtain the vibronic transition intensities we calculate the equilibrium geometries and vibrational modes of the ground and excited electronic surfaces. The calculated vibronic transition intensities of trans−stilbene are in good agreement with the observed ones. The calculated torsional contributions enable us to assign some of the lines in the spectrum of trans−stilbene and suggest the possibility of deviations from planarity in the ground state equilibrium conformation. The observed diffuse structure of the π→π* transition of cis−stilbene is reproduced and the contributions to photoisomerization of torsional and out−of−plane modes are considered.
TL;DR: In this paper, the effects of variations in the type and size of the basis set on the SCF and CI energies and on computed first-order one-electron properties have been examined.
Abstract: Ab initio self‐consistent field and configuration interaction calculations have been carried out for the ground state of the water molecule near its experimental equilibrium geometry. Several contracted Gaussian (CGTO) and Slater type (STO) basis sets have been used, and the effects of variations in the type and size of the basis set on the SCF and CI energies and on computed first‐order one‐electron properties have been examined. The CI calculations included all single and double excitation configurations relative to the SCF function. The largest basis set studied, a 39‐STO (5s4p2d/3s1p) basis, provided an SCF energy of −76.064226 hartree, which is about 3 mhartree above the estimated Hartree–Fock limit, and a CI energy of −76.339802 hartree, which accounts for 74.5% of the estimated total correlation energy. The SCF and CI one‐electron property expectation values for this basis are generally within 5%–10% of the experimental values. Ionization potentials, binding energy, and pair‐correlation energies ha...
TL;DR: The total dissociation cross section for methane was reported for electron energies between 10 and 500 eV as discussed by the authors, and a maximum cross section of 4×10−16 cm2 occurred at 85 eV.
Abstract: The total dissociation cross section for methane is reported for electron energies between 10 and 500 eV. A maximum cross section of 4×10−16 cm2 occurs at 85 eV. Dissociation into ionic and neutral fragments have about equal probability for energies between 50 and 500 eV. At lower energies most of the fragments are uncharged, ground state, or long lived excited state molecules. The experimental technique is discussed in detail and criteria established for determining gases for which similar methods can be applied.
TL;DR: In this paper, fixed-frequency laser photoelectron spectrometry has been utilized to study the ions Si, SiH, and SiH−2, and their binding energies determined.
Abstract: Fixed−frequency laser photoelectron spectrometry has been utilized to study the ions Si−, SiH−, and SiH−2. In each case, the photodetached electron energy spectrum consists primarily of sharp, easily assignable peaks. The electron affinities of Si, SiH, and SiH2 have been determined to be (1.385±0.005) eV, (1.277±0.009) eV, and (1.124±0.020) eV, respectively. Two bound excited states attributed to 2D and 2P terms have been observed for Si−, and their binding energies determined. Similarly, two bound excited states, assigned to 1Δ and 1Σ+ symmetry, have been discovered in SiH−. The internuclear distance re in the ground state of SiH− has been determined by a Franck−Condon factor analysis to be (1.474±0.004) A. In addition, spectroscopic constants of the excited states have been deduced. Transitions from the ground state of SiH− to both the 1A1 and 3B1 states of SiH2 have been observed; unlike the case of CH2, the 1A1 state is the lower in energy.
TL;DR: A generalization of the transition state technique introduced by Slater for the calculation of many‐electron relaxation effects accompanying electronic excitations in molecules and molecular simulations of solids shows that excitation energies of somewhat greater accuracy are obtained from self‐consistent calculations performed for transition states corresponding to 2/3 of the transitions.
Abstract: We present a generalization of the transition state technique introduced by Slater for the calculation of many‐electron relaxation effects accompanying electronic excitations in molecules and molecular simulations of solids. By making use of ground state information (which is generally available but not used in the Slater formulation) and transition states which are computationally cheaper (due to being closer to the ground state), the generalization permits the evaluation of excitation energies to be improved in any of three ways: (1) comparable accuracy for less computation; (2) improved accuracy for comparable computation; and (3) full Δ‐SCF accuracy can be approximated with arbitrary precision with additional computation. In particular, we show that excitation energies of somewhat greater accuracy are obtained from self‐consistent calculations performed for transition states corresponding to 2/3 of the transition rather than 1/2 of the transition as in the original formulation by Slater.
TL;DR: In this article, the ground state energies of the ν3 band of methane, 12CH4, were determined using combination difference relations using pairs of transitions having the same upper state energy level (forbidden-allowed and forbidden-forbidden pairs were used), with uncertainties of about 0.001 cm−1.
TL;DR: In this article, cross-beam studies of chemiionization in thermal energy collisions of helium, neon, argon, and krypton metastable atoms with ground state atoms and molecules (Ar, Kr, Xe, N2, H2, O2, NO, CO, CO2, and N2O) are described.
Abstract: Crossed beams studies of chemiionization in thermal energy collisions of helium, neon, argon, and krypton metastable atoms with ground state atoms and molecules (Ar, Kr, Xe, N2, H2, O2, NO, CO, CO2, and N2O) are described. Branching ratios are presented and in some cases absolute total ion production cross sections have been measured.
TL;DR: In this article, the stability of CO2− depends strongly on whether it is formed near the equilibrium bond angle (135°), the most stable situation, or at significantly different angles.
Abstract: SCF ab‐initio computations are performed for the ground states of CO2 and CO2−. The CO2 and CO2− potential surfaces have been obtained over a large region of space; in particular, the intersection of these two surfaces. Our results predict that the stability of CO2− depends strongly on whether it is formed near the equilibrium bond angle (135°), the most stable situation, or at significantly different angles. The calculations show that the 6a1 molecular orbital of CO2− is diffuse in character and that the computed equilibrium geometry (bond angle, 135.3°, bond length, 2.35 bohr) and electron affinity (−0.36 eV) are consistent with experiment.
TL;DR: In this paper, the binding energies for helium-like ions of variable dimensionality (D) with the wave functions A = e+-+&i-«.&+e~-«i-0&.
Abstract: %'e calculate binding energies for heliumlike ions of variable dimensionality (D) with the wave functions A = e&-+&i-«.&+e~-«i-0&. & and 8 =A(1+ cA»). The binding energy decreases with increasing D. Functions A and 8 predict \"critical binding dimensionalities\" at D= 3.99 and 4.89, respectively, above which there is no binding in the hydride anion. The exact groundstate binding energy at D = 5 is shown to be equal to that of the doubly excited 2p' 'I\" state into in three dimensions. By \"dimensionality scaling\" of atomic units the D = 1 atom is transformed the 5-function model for which exact energies are known. In the infinite dimensional limit, function A predicts no exchange contribution to binding for nuclear charge Z & Q2, with a. +P only for Z & g2.
TL;DR: In this article, the potential energy curve for the electronic ground state of the hydrogen molecule has been recomputed for intermediate and large internuclear separations, and the largest improvement amounts to 5.5 cm −1, and was obtained in the vicinity of R = 4.4a.
01 Sep 1975
TL;DR: In this paper, it was shown that the appearance of two M binding energies is not in itself evidence for electronic ground-state asymmetry in a mixed-valence compound, and a model was proposed from which quantitative predictions were made.
Abstract: It has previously been assumed that an ESCA measurement on a mixed-valence-e.g., M(II)-M(III) - compound which yields two peaks for an inner-shell M ionization at energies close to those measured for separate M(II) and M(III) ions provides direct evidence that the complex has an unsymmetrical (trapped-valence) ground state rather than one in which the electrons are symmetrically delocalized. This assumption is incorrect. A complex which has a symmetrical ground state will have two accessible unsymmetrical photoionized states owing to electron relaxation in the strong field of the core hole. For a range of values of binding energy differences and electron coupling parameters, the photoionized states will be very nearly localized and the peak separation for a complex with delocalized ground state will be close to that for isolated M(II) and M(III) ions. The appearance of two M binding energies is thus not in itself evidence for electronic ground-state asymmetry in a mixed-valence compound. A model is proposed from which quantitative predictions are made.
TL;DR: In this paper, a pulsed tunable dye laser was used to obtain the steady state spectra of NH2 and collisional energy transfer was observed within the (2A1) excited electronic state.
Abstract: Time resolved fluorescence from the first excited (2A1) state of NH2 has been observed following excitation of the radical in its ground state by means of a pulsed tunable dye laser. Specific rotational levels within a number of vibronic states were populated, decay rates measured as a function of total pressure for a variety of added gases, and zero pressure lifetimes and collisional de‐excitation rates evaluated. Measured zero pressure lifetimes are good approximations to the vibrational state radiative lifetimes, typically 10 μsec for the (0, 9, 0) state. Collisional de‐excitation rate constants were measured as 1.0×10−9 cm3 molecule−1⋅sec−1 for NH3, independent of vibronic state, and for the Σ (0, 9, 0) level were found for other gases in the ratio NH3:CO:H2:N2:CH4:Ar:He=1.0:0.47:0.46:0. 40:0.30:0.152:0.145. Using excitation by a tunable cw dye laser, steady state spectra of NH2 have been obtained and collisional energy transfer observed within the (2A1) excited electronic state of NH2. Transfer was o...
TL;DR: In this article, a kinetic study of C(23PJ) generated by the repetitive pulsed irradiation of carbon suboxide in the Schumann region was presented, where ground state carbon atoms were monitored photoelectrically by resonance absorption at λ≈ 166 nm in the time-resolved mode.
Abstract: A kinetic study of C(23PJ), generated by the repetitive pulsed irradiation of carbon suboxide in the Schumann region, is presented. The ground state carbon atoms were monitored photoelectrically by resonance absorption at λ≈ 166 nm in the time-resolved mode. The resulting photoelectric signals were translated into kinetic data by means of rapid response precision logarithmic circuitry, signal averaging and computerised analysis of the raw data. Rate data for the removal of C(23PJ) in the presence of the added reactant gases H2, O2, NO, N2O, CO2, H2O and C3O2 are reported and these are compared with those derived from other studies involving vacuum ultra-violet absorption spectroscopy, principally “single-shot” flash photolysis experiments involving oscilloscopic recording of attenuation of resonance radiation and plate photometry. The advantages of the present method, premitting detailed investigation of the atomic decays, are demonstrated.
TL;DR: In this article, three independent experiments were performed in order to elucidate low-energy electron collisions on hydrogen halides, showing that the formation of Cl− and Br− shows a steep onset near threshold and structure at higher energies.
Abstract: Three independent experiments are performed in order to elucidate low‐energy electron collisions on hydrogen halides. The formation of Cl− and Br− shows a steep onset near threshold and structure at higher energies. This structure occurs at the energies of vibrational levels of the X 1Σ+ ground state of the hydrogen halide. The transmission spectrum of HBr shows structure at the position of the v=1 level of the X 1Σ+ state. In addition, transmission spectra show that the vibrational cross section to v=1 in all the hydrogen halides rises steeply near threshold and levels off about 60 meV above threshold. A trapped‐electron experiment in HCl substantiates this observation and in addition, gives the order of magnitude of the vibrational cross section near threshold (2×10−16–2×10−15 cm2).
TL;DR: In this article, the energy functional for the Skyrme density-dependent force was used to calculate the interaction potential between two 16 O nuclei, and a two-centre harmonic oscillator potential was employed to construct the density and kinetic energy density of the ground state of the combined system and of the separated nuclei.
TL;DR: In this paper, integral and differential cross sections for pure rotational and simultaneous rotational−vibrational excitation of H2 by Li+ impact have been computed following the coupled−channel formalism using two different SCF potential energy hypersurfaces and a CI hypersurface at 0.6 and 1.2 eV.
Abstract: Integral and differential cross sections for pure rotational and simultaneous rotational−vibrational excitation of H2 by Li+ impact have been computed following the coupled−channel formalism using two different SCF potential energy hypersurfaces and a CI hypersurface at 0.6 and 1.2 eV. Sensitivity of integral cross sections to (a) choice of ab initio potential energy surface and (b) expansion length of a Legendre polynomial representation of one of the energy surfaces is examined. It is seen that preparation of H2 in the v = 0, j = 2 state leads to four− and fivefold increases in excitation cross sections to the v′ = 1, j′ = i, i = 0,2,4 states relative to excitation of ground state (v = 0, j = 0) H2. Differential cross sections are reported at 1.2 eV for up to five quantum rotational and for vibrational transitions on one of the energy hypersurfaces. All angular distributions required for determining ratios (inelastic : elastic) of differential cross sections needed for comparison with recent time−of−fli...
TL;DR: In this article, the Coulomb wave and Green function were employed in the momentum representation of double photoionization and photoionisation accompanied by excitation of He-like atomic systems.
Abstract: Cross sections of such processes as double photoionization and photoionization accompanied by excitation of He-like atomic systems are investigated in the limit of high, but still not relativistic, photon energies. In addition to total cross sections electron energy and angular distributions are also obtained. Coulomb wave and Green functions were employed in the momentum representation. Results for the total double ionization cross section as a function of photon energy are close to those obtained by predecessors with much more complicated ground state wavefunctions. The cross section of ionization with simultaneous excitation differs considerably from those obtained before. Angular and energy distributions of ionized electrons, are, to this extent, investigated for the first time.