A remarkable match of optical response in the amorphous-crystalline and zinc blende-rock salt phase pairs of GeTe.

Despite a large amount of theoretical and experimental work performed so far, the search of phase change materials (PCMs) is done with use of numerical modeling. However, it is not fully clear how and why the phase change translates into the optical contrast. In this work, we argue that a key prerequisite for a material to have a pronounced difference in optical properties between crystalline and glassy phases of PCM is the similar contrast between the observed crystalline and (may be experimentally inaccessible) parent crystalline polymorph of the glassy phase.

Electronic Structure and d-d Spectrum of Metal-Organic Frameworks with Transition-Metal Ions.

The electronic structure of metal-organic frameworks (MOFs) containing transition metal (TM) ions represents a significant and largely unresolved computational challenge due to limited solutions to the quantitative description of low-energy excitations in open d-shells. These excitations underpin the magnetic and sensing properties of TM MOFs, including the observed remarkable spin-crossover phenomenon. We introduce the effective Hamiltonian of crystal field approach to study the d-d spectrum of MOFs containing TM ions; this is a hybrid QM/QM method based on the separation of crystal structure into d- and s,p-subsystems treated at different levels of theory.

Local perturbations of periodic systems. Chemisorption and point defects by GoGreenGo.

We present a software package GoGreenGo-an overlay aimed to model local perturbations of periodic systems due to either chemisorption or point defects. The electronic structure of an ideal crystal is obtained by worldwide-distributed standard quantum physics/chemistry codes, and then processed by various tools performing projection to atomic orbital basis sets. Starting from this, the perturbation is addressed by GoGreenGo with use of the Green's functions formalism, which allows evaluating its effect on the electronic structure, density matrix, and energy of the system.

Solid-state quantum chemistry with ΘΦ (ThetaPhi): Spin-liquids, superconductors, and magnetic superstructures made computationally available.

We present a standalone ΘΦ (ThetaPhi) package capable to read the results of ab initio DFT/PAW quantum-chemical solid-state calculations processed through various tools projecting them to the atomic basis states as an input and to perform on top of this an analysis of so derived electronic structure which includes (among other options) the possibility to obtain a superconducting (Bardeen-Cooper-Schrieffer, BCS), spin-liquid (resonating valence bond, RVB) states/phases as solutions of the electronic structure problem along with the magnetically ordered phases with an arbitrary pitch (magnetic superstructure) vector. Remarkably, different solutions of electronic-structure problems come out as temperature-dependent (exemplified by various superconducting and spin-liquid phases) which feature is as well implemented. All that is exemplified by model calculations on 1D chain, 2D square lattice as well as on more realistic superconducting doped graphene, magnetic phases of iron, and spin-liquid and magnetically ordered states of a simplest nitrogen-based copper pseudo-oxide, CuNCN, resembling socalled metal-oxide framework (MOF) phases by the atomic interlinkage.

Deductive molecular mechanics of four-coordinated carbon allotropes.

Deductive molecular mechanics is applied to study the relative stability and mechanical properties of carbon allotropes containing isolated σ-bonds. Our approach demonstrates numerical accuracy comparable to that of density-functional theory, but achieved with dramatically lower computational costs. We also show how the relative stability of carbon allotropes may be explained from a chemical perspective using the concept of strain of bonds (or rings) in close analogy to theoretical organic chemistry.