Masayuki Hasegawa

Theory of Compressibility of Simple Liquid Metals

Pressure and compressibility of simple metals such as alkali metals, Zn, Al and Pb are calculated in the liquid state near the triple point, using the pseudopotential formalism for electron-ion interaction. Effective ion-ion interaction is defined naturally by calculating the total energy of metals to the second order of the electron-ion pseudopotential and its contributions to pressure and bulk modulus are calculated separately by the use of the so-called pressure equation of state modified properly to include the effects of the density-dependence (due to the electronic screening effect) of the effective ion-ion potential. It is found that these contributions are much larger (of more repulsive nature) than those estimated by using the Percus-Yevick solution for the hard-sphere model. The effects of the density dependence of the ion-ion interaction are found quite important for the pressure in alkali metals. Comparison of the calculated values of compressibility with experiments is made and the agreement ...

Theory of Plasmon Damping in Metals. I. General Formulation and Application to an Electron Gas

A new general formulation for calculating the wave-number dependence of plasmon damping in metals, including the effects of both the electron-electron and the electron-ion interactions, is presented. As an important application of the general formalism, the case of an electron gas is investigated. The detailed calculation of the probabilities of plasmon decay by producing two electron-hole pairs is made. The effects of exchange processes are also investigated. The numerical result for the q 2 coefficient of the plasmon damping rate is considerably smaller than that obtained by previous theories. The process of plasmon decay via excitation of one electron-hole pair plus another plasmon is shown to contribute a term of q 6 in contrast with the result of previous theories which predicted it to be of q 4 . The comparison with characteristic energy loss experiments is also discussed briefly.

First principles calculations for electronic band structure of single-walled carbon nanotube under uniaxial strain

Electronic band structures of single-walled carbon nanotubes (SWNTs) are studied using first principles ultrasoft pseudopotential with plane wave basis. We find that band gap values of relaxed SWNTs in the generalized gradient approximation significantly differ from those obtained in the local density approximation for the exchange-correlation functional. In addition, it is shown that electronic band structures and total energies of SWNTs are strongly correlated with axial strain.

VARIATIONAL PERTURBATION CALCULATIONS FOR THE PHASE DIAGRAM OF SYSTEMS WITH SHORT-RANGED INTERACTIONS

A variational perturbation theory based on the Gibbs–Bogoliubov inequality is used to predict the phase behavior of systems with short-ranged interactions. We are primarily concerned with the disappearance of a stable liquid phase and the occurrence of an isostructural solid–solid transition, and consider two model systems interacting via a hard-sphere attractive Yukawa (HSAY) potential and a so-called m−n potential, a natural extension of the 12−6 Lennard-Jones potential to higher powers. In the variational calculations, a consistent treatment of the fluid and solid phases is aimed at and the hard-sphere system is used as the reference system for both phases. The predicted phase diagrams for the HSAY system with not very short-ranged potential are confirmed to be in good agreement with essentially the same calculations by Hagen and Frenkel [J. Chem. Phys. 101, 4093 (1994)]. The predicted isostructural solid–solid transition for this system, which occurs for a very short-ranged potential, are somewhat dif...

A new simple pseudopotential with applications to liquid metal structure factor calculations

Abstract The self-consistent fields for 24 simple metal atoms have been calculated and unscreened so as to obtain the electron-ion potentials. The results, to good accuracy, take the form - (z/r) [1 + a exp(− br)] from well below the Ashcroft radius rc to well above it, and the parameters a,b show systematic, physically interpretable trends. It will sometimes be profitable to generalise the Ashcroft pseudopotential so as to incorporate explicitly the above ionic tail. Thus, a simple local form can be retained with a wider range of applicability. Concentration fluctuations in liquid Naue5f8Cs are used to illustrate the point.

Monte Carlo simulation study of the high-temperature phase diagram of model C60 molecules

The constant-NVT Monte Carlo simulation is performed for model C60 molecules interacting via the Girifalco potential and a full free-energy analysis is made to predict the high-temperature phase diagram. The repulsive part of the C60 potential is very steep and the attractive part is relatively short-ranged. For such a system accurate computations of the virial pressure are difficult in simulations and it is argued that the discrepancies among the previous results for the phase diagram of C60 can partly be attributed to the uncertainties of the virial pressure involved in simulations. To avoid this difficulty we take the energy route to calculate equation of state (EOS), in which the absolute (Helmholtz) free energy is obtained by performing isochoric integration of the excess internal energy. A difficulty of the energy route in the high-temperature limit is resolved by the aid of an analytic method. The exact second and third virial coefficients are also used in the analysis of the fluid EOS. The pressur...

The dependence of the phase diagram on the range of the attractive intermolecular forces

A density functional theory of freezing combined with a thermodynamically consistent integral equation method is used to investigate the phase behaviour of systems interacting via the m-n potential with m = 2n, o(r) = 4e[(σ/r) 2n -(σ/r) n ] (n = 6, 8, 10 and 12) and rigid C 60 molecules interacting via the Girifalco potential. It is found that the liquid-vapour coexistence region is gradually suppressed as the attractive part of the potential becomes short range with increasing n and the coexistence ceases to occur at n 11. The m-n potential with n = 11-12 is similar to the Girifalco potential and the two yield similar phase diagrams. It is also found that the phase diagram of C 60 calculated for a truncated potential is qualitatively in agreement with the corresponding Monte Carlo (MC) simulations of Hagen et al, which have predicted nonexistence of the liquid phase in contrast to the molecular dynamics (MD) simulations of Cheng et al. These results suggest the importance of treating the long-range tail of the potential correctly and provide a partial explanation for the discrepancy between the MC and MD simulations.

Theory of Plasmon Damping in Metals. II. Effects of Electron-Ion Interaction

Effects of electron-ion interaction on the plasmon damping in metals are investigated by using a general formulation developed in a previous paper. Damping of a plasmon with small wavenumber q is mainly determined by the processes in which the plasmon dacays into (i) one electron-hole pair by interband transition and (ii) one electron-hole pair with simultaneous absorption or emission of a phonon. These processes give negative q 2 -coefficient of damping in the small wavenumber region. On the other hand, the process in which the plasmon decays into another plasmon with simultaneous absorption or emission of a phonon gives the damping nearly proportional to q . As a whole, with including the contribution of the electron-electron interaction discussed in I, plasmon half-width in Al slightly decreases as q increases in the small q region, while the damping in Na slightly increases with q .

Theory of Thermodynamic Properties of Liquid Metals

Thermodynamic properties of simple liquid metals investigated from the fundamental point of view of the electron theory of metals. Modified from of the pressure equation appropriate to liquid metals is applied to the calculations of the thermal pressure coefficient and the thermal expansion coefficient of simple metals using the pseudopotential formalism for the electron-ion interaction. Comparisons of the predictions and experiments are made and the agreement is found satisfactory for the simpler metals.

Intermolecular potential and the equation of state of solid C60

First-principles total-energy calculations are performed for the low-temperature ordered phase of solid C60 in the wide range of lattice parameter. The intermolecular potential obtained from these calculations is successfully modeled in terms of the interaction between carbon atoms on different C60 molecules and the multipole Coulombic interaction between molecules. This model enables us to calculate structural and thermodynamic properties of both the orientationally ordered and disordered phases in a consistent manner. We find that the equation of state at finite temperature obtained for this potential is not in good agreement with experiments and the intermolecular potential is much shallower than that expected from the experimental heat of sublimation. These discrepancies are interpreted as arising from the limited capability of the density-functional calculations to appropriately incorporate the effect of electron correlations at large separation, which is responsible for the long-range behavior of th...