Quasirelativistic methods

A comparative study of quasirelativistic equations used in atomic structure calculations has been performed. A uniform derivation of all the equations is presented, and some of their specific features are discussed in detail. Electron density distributions, orbital energies, and expectation values of rⁿ obtained with different methods are compared with the ones resulting from the Schrödinger and Dirac equations. The most accurate are found to be the equations of Wood and Boring and of Barthelat, Pelissier, and Durand. (They reproduce almost exactly the Dirac electron densities and expectation values.) The simplest, though least accurate, equation is proposed by us. It gives the relativistic energy corrections with about 6% accuracy and retains exactly the form of the nonrelativistic Schródinger equation. Consequently, its application in analytical SCF-CI calculations does not require any additional integral calculation.     

A renormalization group model with non-Gaussian fixed point

We apply short distance scaling to the Wick square of a massive free time zero field and show that the characteristic functionals of the suitably renormalized fields have a short distance limit. The properties of the limiting characteristic functionals allow us to find a class of the other renormalization group invariant processes. They are all non-Gaussian, but can be expressed by superposition of the Gaussians. We also discuss the test function spaces and the pointwise limit of the n-point functions.     

Diffusion processes with ultrametric jumps

In the theory of spin glasses the relaxation processes are modelled by random jumps in ultrametric spaces. One may argue that at the border of glassy and nonglassy phases the processes combining diffusion and jumps may be relevant. Using the Dirichlet form technique we construct a model of diffusion on the real line with jumps on the Cantor set. The jumps preserve the ultrametric feature of a random process on unit ball of 2-adic numbers.     

Grad’s 13 Moment Equations in a Modified Form

We describe a hierarchy of formal expansions that represent the Fourier transform of a solution of the Boltzmann equation. The constructed approximations are based on the family of weighted Taylor expansions. The first two representations correspond to the Maxwellian and to the Gaussian expansions. The third representation has a weight that generalizes the Gaussian and it depends on the first 13 moments of the Boltzmann density f. It can be shown that this weight is Galilean invariant and it is close to the Gaussian, providing that the heat fluxes are not too large. The 13 moment weight yields a revised form of Grad’s 13 moment expansion for the Boltzmann equation. In search for the entropy dissipation inequality, we also examine the relation between Levermore’s 14 moment and Grad’s 13 moment expansion. First, we show that the coefficients of the Godunov potential are described by a system of partial differential equations, with coefficients that depend on the Fourier transform of the Levermore’s density fΛ. Then, we argue that the same Taylor expansion exploited in the Grad’s scheme can be used to approximate Levermore’s 14 moment density. We also show that the weighted Taylor expansions are related to a formal solution of the Hamburger problem.