UppASD
Uppsala Atomistic Spin Dynamics - simulating atomistic spin dynamics
What is UppASD
The Uppsala Atomistic Spin Dynamics (UppASD) code is used to simulate atomistic spin dynamics at finite temperatures. This code makes it possible to describe magnetisation dynamics on an atomic level.
Simulations with UppASD are often performed as part of multiscale modelling of magnetic materials. Modern implementations of first principles density functional theory (DFT) can be used to calculate ground state properties of a crystalline or nanoscale magnetic material, but do not by themselves give access to the dynamics of the spin polarisation over extended time and length scales. Atomic magnetic moments can be defined for each lattice site as the integral of the magnetisation density over atomic volumes, and thereby constitute a coarse grained representation of the magnetisation. Over nanometer length scales, the interactions between magnetic moments are mainly of quantum mechanical origin. The strength of these interactions can be calculated from the DFT ground state solution of the material. The magnetic moments and their interactions are the required ingredients for constructing materials-specific effective magnetic Hamiltonians.
The magnetic phase diagram and thermodynamical properties of a magnetic Hamiltonian can be investigated with techniques for Monte Carlo simulations. Alternatively, the equations of motion of the Hamiltonian can be investigated. In the atomistic spin-dynamics method, the dynamics of the Hamiltonian are treated in the semiclassical limit. This enables simulations that readily can consist of hundreds of thousands of spins evolved over hundreds of picoseconds. An important capability of atomistic approaches is that short-ranged local interactions and correlations, and the spin texture over longer distances, can be studied simultaneously.
In condensed matter physics, a key knob for tuning the properties of materials is to change their chemical composition. For magnetic materials, doping can be used to alter the interactions between magnetic moments, as well as the magnetocrystalline anisotropy. Modelling of chemically disordered materials is, in general, more demanding than modelling pristine material with perfect crystalline structure. The UppASD code supports the modelling of disordered material. When chemical disorder is treated on atomic length scales, the computational effort can drastically increase given that averaging needs to be done over simulations of different realizations of the disorder. In methods for simulating coupled spin-lattice dynamics the atomistic spin-dynamics method is augmented to include also the ionic motion degrees of freedom. Support for spin-lattice dynamics simulations has been implemented in UppASD.
UppASD development partners
UppASD is developed by researchers from the Division of Materials Theory at Uppsala University, Uppsala, as well as PDC and the Department of Applied Physics at the KTH Royal Institute of Technology, Stockholm.
Current developments
Coming up shortly...
Links
- UppASD code on GitHub: github.com/UppASD/UppASD
Contact
For more information about UppASD development at PDC, you are welcome to contact:
