F. J. Pinski

Self‐consistent electronic structure of disordered Fe0.65Ni0.35

We present the results of the first ab initio calculation of the electronic structure of the disordered alloy Fe0.65Ni0.35. The calculation is based on the multiple‐scattering coherent‐potential approach (KKR‐CPA) and is fully self‐consistent and spin polarized. Magnetic effects are included within local‐spin‐density functional theory using the exchange‐correlation function of Vosko–Wilk–Nusair. The most striking feature of the calculation is that electrons of different spins experience different degrees of disorder. The minority spin electrons see a very large disorder, whereas the majority spin electrons see little disorder. Consequently, the minority spin density of states is smooth compared to the very structured majority spin density of states. This difference is due to a subtle balance between exchange splitting and charge neutrality.

A first-principles study of phase stability in NiAl and NiTi alloys

Abstract The thermodynamic stability of the b.c.c.- and f.c.c.-based ordered phases of NiTi and NiAl has been studied with a highly accurate first-principles electronic structure method. The occurrence of a martensitic transformation in NiAl B2 ordered intermetallic alloys will be discussed and related to the existence of intermediate structures between b.c.c.- and f.c.c.-based phases. It will be shown that closely related ordered structures can exist on f.c.c. and b.c.c. lattices in the composition range where the transformation occurs. A variety of antiphase boundaries in the B2 and L12 structures will be examined and the pertinent energies will be compared with experimental data. In addition, the rather unusual appearance of the NiTi B2 ordered structure in the phase diagram will be discussed.

Theoretical study of phase stability in Ni-Al and Ni-Ti alloys

The thermodynamic stability of the bcc and fcc based ordered phases in Ni-Ti and Ni-AI has been studied with a highly accurate first-principles electronic structure method. The occurrence of a martensitic transformation in Ni-AlB2 ordered intermetallic alloys is discussed with relation to the existence of intermediate structures between bcc and fcc based phases. It is shown that closely related ordered structures can exist on fcc and bcc lattices in the composition range where the transformation occurs. The Ni-rich side of the Ni-Al phase diagram has been computed, and a comparison with a recent assessment is made. In addition, the rather unusual appearance of the NiTi B2 ordered structure in the phase diagram is discussed.

Transition paths in molecules at finite temperature

In the zero temperature limit, it is well known that in systems evolving via Brownian dynamics, the most likely transition path between reactant and product may be found as a minimizer of the Freidlin–Wentzell action functional. An analog for finite temperature transitions is given by the Onsager–Machlup functional. The purpose of this work is to investigate properties of Onsager–Machlup minimizers. We study transition paths for thermally activated molecules governed by the Langevin equation in the overdamped limit of Brownian dynamics. Using gradient descent in pathspace, we minimize the Onsager–Machlup functional for a range of model problems in one and two dimensions and then for some simple atomic models including Lennard-Jones seven-atom and 38-atom clusters, as well as for a model of vacancydiffusion in a planar crystal. Our results demonstrate interesting effects, which can occur at nonzero temperature, showing transition paths that could not be predicted on the basis of the zero temperature limit. However the results also demonstrate unphysical features associated with such Onsager–Machlup minimizers. As there is a growing literature that addresses transition path sampling by related techniques, these insights add a potentially useful perspective into the interpretation of this body of work.

Kullback-Leibler approximation for probability measures on infinite dimensional spaces

In a variety of applications it is important to extract information from a probability measure

The Electronic Structure and the State of Compositional Order in Metallic Alloys

\mu

A Function Space HMC Algorithm With Second Order Langevin Diffusion Limit

on an infinite dimensional space. Examples include the Bayesian approach to inverse problems and (possibly conditioned) continuous time Markov processes. It may then be of interest to find a measure

A first-principles study of phase stability in Ni-Al and Ni-Ti alloys

\nu

Algorithms for Kullback--Leibler Approximation of Probability Measures in Infinite Dimensions

, from within a simple class of measures, which approximates

Local density theory of magnetism and its interrelation with compositional order in alloys

\mu