The <scp>KOALA</scp> program: Wavefunction frozen‐density embedding
Sebastian Höfener
Abstract
Abstract 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.