A local Bayesian optimizer for atomic structures

A local optimization method based on Bayesian Gaussian Processes is developed and applied to atomic structures. The method is applied to a variety of systems including molecules, clusters, bulk materials, and molecules at surfaces. The approach is seen to compare favorably to standard optimization algorithms like conjugate gradient or BFGS in all cases. The method relies on prediction of surrogate potential energy surfaces, which are fast to optimize, and which are gradually improved as the calculation proceeds. The method includes a few hyperparameters, the optimization of which may lead to further improvements of the computational speed.Comment: 10 pages, 5 figure

Linear density response function in the projector-augmented wave method: Applications to solids, surfaces, and interfaces

We present an implementation of the linear density response function within the projector-augmented wave (PAW) method with applications to the linear optical and dielectric properties of both solids, surfaces, and interfaces. The response function is represented in plane waves while the single-particle eigenstates can be expanded on a real space grid or in atomic orbital basis for increased efficiency. The exchange-correlation kernel is treated at the level of the adiabatic local density approximation (ALDA) and crystal local field effects are included. The calculated static and dynamical dielectric functions of Si, C, SiC, AlP and GaAs compare well with previous calculations. While optical properties of semiconductors, in particular excitonic effects, are generally not well described by ALDA, we obtain excellent agreement with experiments for the surface loss function of the Mg(0001) surface with plasmon energies deviating by less than 0.2 eV. Finally, we apply the method to study the influence of substrates on the plasmon excitations in graphene. On SiC(0001), the long wavelength $\pi$ plasmons are significantly damped although their energies remain almost unaltered. On Al(111) the $\pi$ plasmon is completely quenched due to the coupling to the metal surface plasmon.Comment: 11 pages, 8 figures, articl

Modelling and Analysis of Distributed Program Execution in BETA Using Coloured Petri Nets

Recently, abstractions supporting distributed program execution in the object-oriented language BETA have been designed. A BETA object on one computer may invoke a remote object, i.e., an object hosted by another computer. In this project, the formalism of Coloured Petri Nets (CP-nets or CPN) is used to describe and analyse the protocol for remote object invocation. In the first place, we build a model in order to describe, understand, and improve the protocol. Remote object invocation in BETA is modelled on the level of threads (lightweight processes) with emphasis on the competition for access to critical regions and shared resources. Secondly, the model is analysed. It is formally proved that it has a set of desirable properties, e.g., absence of dead markings.Topics: Systemdesign and verfication using nets; higher-level nets models; computer tools for nets; experience with using nets, case studies; application of nets to protocols

Leading or Being Led: The Authentic Leadership Dilemma

This chapter explores how industrial PhD students are engaged in authenticleadership processes while coping with challenges through self-leadership.The authors illustrate how self-leadership can be a helpful approach tomanaging the leading-and-being-led dilemma. They argue thatself-leadership is a process of goal achievement in collaboration with keystakeholders and, therefore, an important aspect of authentic leadership. Theauthors identify four aspects of self-leadership that influence authenticity:roles, resources, relations and results. Kringelum, Mortensen and Holmgrencall for research into the emergence of self-leadership and authentic leadership,the leadership capabilities required and the double-sidedness anddilemmas inherent in such emergences across different contexts