Quantum Physics and Chemistry Department (QPCD)

We develop the two-step technology to calculate the electronic structure and properties of materials as well: first, we calculate the periodic structure of a perfect crystal using medium-core semilocal GRPPs for heavy atoms, then we build the “compound-tunable embedding potential” or CTEP (see below) for a chosen crystal fragment. The CTEP method describes with very high accuracy the effect of the environment on a given fragment, and, accordingly, the electronic structure of the crystal fragment itself is also reproduced properly. Finally, a two-component calculation of the crystal fragment ("cluster calculation") is performed using the CTEP embedding potential, precision versions of the relativistic pseudopotentials for heavy atoms, and fairly complete atomic basis sets. Compared to the extended cell methods, point defects (including vacancies, actinides, lanthanides and heavy transition metals) are much simpler considered in materials within the framework of cluster calculations with CTEP and with an accuracy unattainable for computational methods using the periodic boundary conditions (see article [Maltsev et al., Sci.Rep.(2025)]). In the cluster case with CTEP, the computational errors can be less than 0.1 eV for valence energies (~0.01 eV in prospect that is provided by the GRECP and CTEP approximations); it is possible to take into account local symmetry within the fragment that is breaking the crystal one; relativistic effects (including Breit and quantum electrodynamic); electron correlation within the framework of the wave function theory; correctly consider charged fragments of crystals and those including atoms with partially occupied core shells; study the localized (nonlinear) quantum processes, etc.