Peter Steneteg

Temperature dependent effective potential method for accurate free energy calculations of solids

We have developed a thorough and accurate method of determining anharmonic free energies. The technique is based in ab initio molecular dynamics and map a model Hamiltonian to the fully anharmonic ...

Equation of state of paramagnetic CrN from ab initio molecular dynamics

The equation of state for chromium nitride has been debated in the literature in connection with a proposed collapse of its bulk modulus following the pressure-induced transition from the paramagne ...

Wave function extended Lagrangian Born-Oppenheimer molecular dynamics

Extended Lagrangian Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)] has been generalized to the propagation of the electronic wave functions. The techn ...

Vibrational free energy and phase stability of paramagnetic and antiferromagnetic CrN from ab initio molecular dynamics

We present a theoretical first-principles method to calculate the free energy of a magnetic system in its high-temperature paramagnetic phase, including vibrational, electronic, and magnetic contri ...

Extended Lagrangian free energy molecular dynamics

Extended free energy Lagrangians are proposed for first principles molecular dynamics simulations at finite electronic temperatures for plane-wave pseudopotential and local orbital density matrix-based calculations. Thanks to the extended Lagrangian description, the electronic degrees of freedom can be integrated by stable geometric schemes that conserve the free energy. For the local orbital representations both the nuclear and electronic forces have simple and numerically efficient expressions that are well suited for reduced complexity calculations. A rapidly converging recursive Fermi operator expansion method that does not require the calculation of eigenvalues and eigenfunctions for the construction of the fractionally occupied density matrix is discussed. An efficient expression for the Pulay force that is valid also for density matrices with fractional occupation occurring at finite electronic temperatures is also demonstrated.

Role of N defects in paramagnetic CrN at finite temperatures from first principles

Simulations of defects in paramagnetic materials at high temperature constitute a formidable challenge to solid-state theory due to the interaction of magnetic disorder, vibrations, and structural ...

Inviwo — An extensible, multi-purpose visualization framework

To enable visualization research impacting other scientific domains, the availability of easy-to-use visualization frameworks is essential. Nevertheless, an easy-to-use system also has to be adapted to the capabilities of modern hardware architectures, as only this allows for realizing interactive visualizations. With this trade-off in mind, we have designed and realized the cross-platform Inviwo (Interactive Visualization Workshop) visualization framework, that supports both interactive visualization research as well as efficient visualization application development and deployment. In this poster we give an overview of the architecture behind Inviwo, and show how its design enables us and other researchers to realize their visualization ideas efficiently. Inviwo consists of a modern and lightweight, graphics independent core, which is extended by optional modules that encapsulate visualization algorithms, well-known utility libraries and commonly used parallel-processing APIs (such as OpenGL and OpenCL). The core enables a simplistic structure for creating bridges between the different modules regarding data transfer across architecture and devices with an easy-to-use screen graph and minimalistic programming. Making the base structures in a modern way while providing intuitive methods of extending the functionality and creating modules based on other modules, we hope that Inviwo can help the visualization community to perform research through a rapid-prototyping design and GUI, while at the same time allowing users to take advantage of the results implemented in the system in any way they desire later on. Inviwo is publicly available at www.inviwo.org, and can be used freely by anyone under a permissive free software license (Simplified BSD).

Finite-temperature elastic constants of paramagnetic materials within the disordered local moment picture from ab initio molecular dynamics calculations

We present a theoretical scheme to calculate the elastic constants of magnetic materials in the high-temperature paramagnetic state. Our approach is based on a combination of disordered local momen ...