Ground States for Metals from Converged Coupled Cluster Calculations

In this publication we introduce a novel finite-size correction scheme to enable coupled cluster theory for highly accurate materials modeling of metals. Using the example of metal surface energies, which are highly relevant due to their wide range of applications, we demonstrated that this observable can be reliably reproduced with high precision for the first time.

Benjamin Wöckinger successfully passed his Master's exam. In his thesis Orbital Localization in Solids by Riemannian Optimization he implemented and tested different optimization algorithms like BFGS, CG, and SA for orbital localization. Specifically he focused on Intrinsic Bond Orbitals (IBOs). The unitary constraints involved in orbital transformations are inherently satisfied through Riemannian optimization, where cost functions are optimized on Riemannian manifolds. 

Understanding Discrepancies of Wavefunction Theories for Large Molecules

This work demonstrates that one of the most widely-used and accurate quantum chemistry approaches – CCSD(T) theory – in certain cases binds noncovalently interacting large molecular complexes too strongly. Our findings show that a simple yet efficient modification denoted as CCSD(cT) remedies these shortcomings. 

Alexander Rumpf successfully finished his project work "Bonding Orbitals in Solids". In this work he focused on two questions: (1) Does the suitability to construct sparse tensors of localised orbitals deteriorate for materials with small band gaps and diffuse density? (2) Are there trends in the orbital spreads or the sparsity concerning the bandgap or lattice constant?
We will be publishing the intriguing results soon.