TheKOALAprogram: Wavefunction frozen-density embedding

摘要

The KOALA program is presented, and its capabilities are discussed. KOALA is an ab initio code that uses Gaussian-type basis sets with a focus on a treatment of wavefunction embedding methods, for which all subsystems can be relaxed with their corresponding wavefunction density. Among the key features of the program is a Davidson solver that is capable of treating, for example, both linear response for coupled-cluster methods and density functional theory, as well as solving the Z-vector equations for orbital-relaxed ground-state and excited-state molecular properties. This solver is combined with frozen-density embedding, which circumvents the problem of the steep scaling of conventional supermolecular correlation methods, enabling the computation of anisotropic environment effects without using semiempirical methods. A brief theoretical overview is given, and case studies for which the program could be used are discussed, as well as the efficiency for systems containing a total of hundreds of atoms, which can be divided into smaller subsystems.