Density functional theory (DFT) provides a formally exact framework for quantum embedding. The appearance of nonadditive kinetic energy contributions in this context poses significant challenges, but using optimized effective potential (OEP) methods, various groups have devised DFT-in-DFT methods that are equivalent to Kohn–Sham (KS) theory on the whole system. This being the case, we note that a very considerable simplification arises from doing KS theory instead. We then describe embedding schemes that enforce Pauli exclusion via a projection technique, completely avoiding numerically demanding OEP calculations. Illustrative applications are presented using DFT-in-DFT, wave-function-in-DFT, and wave-function-in-Hartree–Fock embedding, and using an embedded many-body expansion.

Projector-based embedding has recently emerged as a robust multiscale method for the calculation of various electronic molecular properties. We present the coupling of projector embedding with quantum mechanics/molecular mechanics modeling and apply it for the first time to an enzyme-catalyzed reaction. Using projector-based embedding, we combine coupled-cluster theory, density-functional theory (DFT), and molecular mechanics to compute energies for the proton abstraction from acetyl-coenzyme A by citrate synthase. By embedding correlated ab initio methods in DFT we eliminate functional sensitivity and obtain high-accuracy profiles in a procedure that is straightforward to apply.

The externally corrected coupled cluster approach with four-and five-body clusters from the CASSCF wave function J. Chem. Phys. 142, 094119 (2015) Methods where an accurate wavefunction is embedded in a density-functional description of the surrounding environment have recently been simplified through the use of a projection operator to ensure orthogonality of orbital subspaces. Projector embedding already offers significant performance gains over conventional post-Hartree-Fock methods by reducing the number of correlated occupied orbitals. However, in our first applications of the method, we used the atomic-orbital basis for the full system, even for the correlated wavefunction calculation in a small, active subsystem. Here, we further develop our method for truncating the atomic-orbital basis to include only functions within or close to the active subsystem. The number of atomic orbitals in a calculation on a fixed active subsystem becomes asymptotically independent of the size of the environment, producing the required O(N 0 ) scaling of cost of the calculation in the active subsystem, and accuracy is controlled by a single parameter. The applicability of this approach is demonstrated for the embedded many-body expansion of binding energies of water hexamers and calculation of reaction barriers of S N 2 substitution of fluorine by chlorine in α-fluoroalkanes. C 2015 AIP Publishing LLC. [http://dx

The BigDFT project started in 2005 with the aim of testing the advantages of using a Daubechies wavelet basis set for Kohn-Sham density functional theory with pseudopotentials. This project led to the creation of the BigDFT code, which employs a computational approach with optimal features for exibility, performance and precision of the results. In particular, the employed formalism has enabled the implementation of an algorithm able to tackle DFT calculations of large systems, up to many thousands of atoms, with a computational eort which scales linearly with the number of atoms. In this work we recall some of the features that have been made possible by the peculiar properties of Daubechies wavelets. In particular, we focus our attention on the usage of DFT for large-scale systems. We show how the localised description of the KS problem, emerging from the features of the basis set, are helpful in providing a simplied description of large-scale electronic structure calculations. We provide some examples on how such simplied description can be employed, and we consider, among the case-studies, the SARS-CoV-2 main protease.

Using electrospray ion beam deposition, we collide a complex molecule Reichardt's Dye (C 41 H 30 NO + ) at low, hyperthermal translational energy (2 -50 eV) with a Cu(100) surface and image the outcome at single-molecule level by Scanning Tunneling Microscopy. We observe bond-selective reaction induced by the translational kinetic energy. The collision impulse compresses the molecule and bends specific bonds, prompting them to react selectively. This dynamics drives the system to seek thermally inaccessible reactive pathways, since the compression timescale (sub-ps) is much shorter than the thermalization timescale (ns), thereby yielding reaction products that are unobtainable thermally