FDE-vdW: A van der Waals Inclusive Subsystem Density-Functional Theory

We present a formally exact van der Waals inclusive electronic structure theory, called FDE-vdW, based on the Frozen Density Embedding formulation of subsystem Density-Functional Theory. In subsystem DFT, the energy functional is composed of subsystem additive and non-additive terms. We show that an appropriate definition of the long-range correlation energy is given by the value of the non-additive correlation functional. This functional is evaluated using the Fluctuation-Dissipation Theorem aided by a formally exact decomposition of the response functions into subsystem contributions. FDE-vdW is derived in detail and several approximate schemes are proposed, which lead to practical implementations of the method. We show that FDE-vdW is Casimir-Polder consistent, i.e. it reduces to the generalized Casimir-Polder formula for asymptotic inter-subsystems separations. Pilot calculations of binding energies of 13 weakly bound complexes singled out from the S22 set show a dramatic improvement upon semilocal subsystem DFT, provided that an appropriate exchange functional is employed. The convergence of FDE-vdW with basis set size is discussed, as well as its dependence on the choice of associated density functional approximant

Patrizi veneziani artisti nel Settecento: l’altro Marcello, Alessandro, pittore e incisore

A profile of the Venetian patrician Alessandro Marcello as a painter and engraver is outlined here for the first time. Alessandro, brother of the more famous Benedetto, was also a musician and a poet (he joined the Academy of Arcadia), as well as a scientist and mathematician: an emblem of the typical Eighteenth-century amateur, open to the most varied experiences. Antonio Maria Zanetti drawed an amusing caricature of him. Alessandro was friend with Rosalba Carriera, who painted his portrait; he executed some frescoes in the church of the Magdalene and in his palace (here illustrated), a series of paintings with Putti engaging in playful scenes, documented by archival findings also published here. A medal with his portrait is indicative of the fame he had achieved in the early Eighteenth century: most interestingly, it presents, on the reverse, a tree with different flowers and fruits, a sign of its interests in various fields

Calculating Hyperfine Couplings in Large Ionic Crystals Containing Hundreds of QM Atoms: Subsystem DFT is the Key

We present an application of the linear scaling Frozen Density Embedding (FDE) formulation of subsystem DFT to the calculation of isotropic hyperfine coupling constants (hfccs) of atoms belonging to a guanine radical cation embedded in a guanine hydrochloride monohydrate crystal. The model systems considered range from an isolated guanine to a 15,000 atom QM/MM cluster where the QM region is comprised of 36 protonated guanine cations, 36 chlorine anions and 42 water molecules. Our calculations show that the embedding effects of the surrounding crystal cannot be reproduced neither by small model systems nor by a pure QM/MM procedure. Instead, a large QM region is needed to fully capture the complicated nature of the embedding effects in this system. The unprecedented system size for a relativistic all-electron isotropic hfccs calculation can be approached in this work because the local nature of the electronic structure of the organic crystals considered is fully captured by the FDE approach