#### Pui-Wai Ma T.-H. Hubert Chan

We have devised a new type of feedforward neural network. It is equivariant with respect to unitary operators $U(n)$. The input and output can be vectors in $\\mathbb{C}^n$ with arbitrary dimension~$n$. No convolution layer is required in our implementation, and we also avoid errors due to truncated higher order terms in Fourier-like transformat…

Preprint Published#### Pui-Wai Ma Sergei L. Dudarev

The concept of elastic dipole tensor of a defect is generalised to enable the treatment of lattice distortions, produced by defects at elevated temperatures. Thermodynamic and statistical mechanics derivations show the feasibility of computing the formation free energy and finite-temperature elastic dipole tensor of a $frac{1}{2}langle 111 rangle$ …

Preprint Published#### Jacob Chapman Pui-Wai Ma Sergei Dudarev

Fundamental flaws in the Heisenberg Hamiltonian are highlighted in the context of its application to BCC Fe, including the particular issues arising when modelling lattice defects. Exchange integrals are evaluated using the magnetic force theorem. The bilinear exchange coupling constants are calculated for all the interacting pairs of atomic ma…

Published#### Pui-Wai Ma S L Dudarev

Using ab initio density function theory calculations, we have determined the structure of self-interstitial atom (SIA) defects in the most commonly occurring face-centred cubic (FCC) metals. The most stable SIA defects in Al, Ca, Ni, Cu, Pd and Ag are the {100} dumbbells whereas octahedral SIA configurations have the lowest energy in Pt, R…

Preprint Published#### Pui-Wai Ma D. R. Mason S. L. Dudarev

We performed ab initio density functional theory simulations of 1/2{111} interstitial dislocation loops, closed and open vacancy loops, {100} interstitial loops and voids in tungsten, using simulation cells involving from 2000 to 2700 atoms. The size of the loops transcends the microscopic scale and reaches the mesoscopic scale where as…

Preprint Published#### Federico Baraglia Pui-Wai Ma

We develop a dynamic model for the evolution of an ensemble of hundreds of interacting irradiation-induced mobile nanoscale defects in a micrometre size sample. The model uses a Langevin defect dynamics approach coupled to a finite element model, treated using the superposition method. The elastic field of each defect is described by its elastic…

Preprint Published#### Pui-Wai Ma S. L. Dudarev

Vacancy formation and migration control self-diffusion in pure crystalline materials, whereas irradiation produces high concentrations of vacancy and self-interstitial atom defects, exceeding by many orders of magnitude the thermal equilibrium concentrations. The defects themselves, and the extended dislocation microstructure formed under irradi…

Preprint Published#### Pui-Wai Ma S. L. Dudarev

For several decades, the striking contradiction between the Huang diffuse scattering experiments, resistivity recovery data, and predictions derived from density functional theory (DFT) remained one of the mysteries of defect physics in molybdenum. Since the nineteen seventies, observations of Huang X-ray diffuse scattering appeared to indicate …

Preprint Published#### Pui-Wai Ma S. L. Dudarev

CALANIE (CALculation of ANIsotropic Elastic energy) program evaluates an elastic interaction correction to the total energy of a localized object, for example a defect in a solid material simulated using an {it ab initio} or molecular statics approach, resulting from the use of periodic boundary conditions. The correction, computed using a fully el…

Preprint Published#### J. Chapman Pui-Wai Ma S. L. Dudarev

Magnetic plasma confinement is a key element of fusion tokamak power plant design, yet changes in magnetic properties of alloys and steels occurring under neutron irradiation are often overlooked. We perform a quantitative study exploring how irradiation-induced precipitation affects magnetic properties of Fe-Cr alloys. Magnetic properties are simu…

Preprint Published