On the calculation of second-order magnetic properties using subsystem approaches in a relativistic framework

Melo

Int J of Quantum Chemistry

et al. 2017

Accurate calculations of some response properties, like the NMR spectroscopic parameters, are quite exigent for the theoretical quantum chemistry models together with the computational codes that are written from them. They need to include a very good description of the electronic density in regions close to the nuclei. When heavy-atom containing systems are studied, those requirements become even higher. Given that relativistic effects must be included in one way or another on the calculation of response properties of heavy-atoms and heavy-atom containing molecules, different schemes were developed during the past decades to include them in as good as possible way. There are some four-component models, which include relativistic effects in a very compact way, although calculations have large time-consumption; one also needs to deal with new and unusual four-component operators. There are also two-component models, which in general may be less accurate, although their application to property calculations on medium-size and large-size molecules are feasible, and they maintain the application of usual operators. In this review, we give the fundamentals of the two-component linear response elimination of small component formalism, LRESC, together with some applications to few selected response properties.New physical insights do appear when the LRESC model is used to analyze the effect of the environment on magnetic shieldings, and when one search for the relativistic extension of well-known nonrelativistic relationships like Flygare's relation among the NMR magnetic shielding and the nuclear spin-rotation constant. A similar relationship is found for the g-tensor and the susceptibility tensor. K E Y W O R D Sg-tensor, NMR, response properties, spin-rotation tensor, two-component methods | I N TR ODU C TI ONThe strong influence of relativistic effects on atomic and molecular response properties of heavy-atom containing molecules was first shown few decades ago.[1] Pyykk€ o included relativistic effects in the calculations of NMR spectroscopic parameters by applying a relativistic model that resemble Ramsey's theory [2] and use relativistic molecular wave function of the relativistically parameterized extended H€ uckel method, REX.[3] Other more elaborated semi-empirical methods and codes were later on used to improve those first results. [4][5][6] The importance of including relativistic effects on the calculation of response properties compelled the theoretical chemists to develop new specific relativistic theories and models. Several formalisms and models appeared in the literature from that time, whose implementations gave more accurate results than that obtained using previous schemes. [7][8][9][10][11][12] We can split them into two broad groups: four-component methods and two-component methods. [12][13][14][15] Even though accurate calculations of response properties of medium-size molecules, meaning molecules containing more than 10 heavy atoms (belonging to the fourth row or below of the Periodic Ta...

Section: Models and Levels Of Approachmentioning

confidence: 99%

“…From Equation 53, the (p-p) contribution to the shielding tensor can be obtained making V 1 5V N and V 2 5V B . With this replacement, the contributions of Table 4 can be expressed as…”

Section: The Nmr Magnetic Shielding Tensormentioning

confidence: 99%

See 1 more Smart Citation

Foundations of the LRESC model for response properties and some applications

Melo

Int J of Quantum Chemistry

et al. 2017

“…These additional contributions, derived by using the chain rule, involve the first-and second-order derivatives of E int with respect to the densities of subsystems -the embedding potential (Eq. 9) and the embedding kernel (see [26] for details). In effect, the property gradient and the electronic Hessian (Eq.…”

Section: Theorymentioning

confidence: 99%

“…As such, one can describe the interactions between the species of interest and its surroundings at a fraction of the cost of applying standard DFT or WFT approaches to the whole system. Contrary to other embedding schemes [19][20][21], such as those in which only the changes in structure due to the environment are considered (mechanical embedding), or where the environment is represented classically (QM/MM) [22], quantum embedding has not yet been extensively used for NMR properties, and this is particularly the case for the frozen density embedding or subsystem DFT methods [23][24][25][26]. This is unfortunate since these approaches have the advantage of allowing for a seamless combination of different electronic structure approaches (DFT and WFT), but also the combination of different Hamiltonians, such as those taking into account relativistic effects.…”

Section: Introductionmentioning

confidence: 99%

Investigating solvent effects on the magnetic properties of molybdate ions (MoO₄2−) with relativistic embedding

Halbert¹,

Olejniczak²,

Vallet³

et al.

Authorea

We investigate the ability of mechanical and electronic density functional theory (DFT)-based embedding approaches to describe the solvent effects on nuclear magnetic resonance (NMR) shielding constants of the 95 Mo nucleus in the molybdate ion in aqueous solution. From the description obtained from calculations with two-and four-component relativistic Hamiltonians, we find that for such systems spin-orbit coupling effects are clearly important for absolute shielding values, but for relative quantities a scalar relativistic treatment provides a sufficient estimation of the solvent effects. We find that the electronic contributions to the solvent effects are relatively modest yet decisive to provide a more accurate magnetic response of the system, when compared to reference supermolecular calculations. We analyze the errors in the embedding calculations by statistical methods as well as through a real-space representation of NMR shielding densities, which are shown to provide a clear picture of the physical processes at play.

Int J of Quantum Chemistry

PCMSolver: An open‐source library for solvation modeling

Remigio

Steindal

Mozgawa

et al. 2018

PCMSOLVER is an open-source library for continuum electrostatic solvation. It can be combined with any quantum chemistry code and requires a minimal interface with the host program, greatly reducing programming effort. As input, PCMSOLVER needs only the molecular geometry to generate the cavity and the expectation value of the molecular electrostatic potential on the cavity surface. It then returns the solvent polarization back to the host program. The design is powerful and versatile: minimal loss of performance is expected, and a standard single point self-consistent field implementation requires no more than 2 days of work. We provide a brief theoretical overview, followed by two tutorials: one aimed at quantum chemistry program developers wanting to interface their code with PCMSOLVER, the other aimed at contributors to the library. We finally illustrate past and ongoing work, showing the library's features, combined with several quantum chemistry programs.The past 10 years have seen theoretical and computational methods become an invaluable complement to experiment in the practice of chemistry. Understanding experimental observations of chemical phenomena, ranging from reaction barriers to spectroscopies, requires proper in silico simulations to achieve insight into the fundamental processes at work. Quantum chemistry program packages have evolved to tackle this everincreasing range of possible applications, with a particular focus on computational performance and scalability. These latter concerns have driven a large body of recent developments, but it has become apparent that similar efforts have to be devoted into the software development infrastructure and practices. Code bases in quantum chemistry have grown over a number of years, in most cases without an overarching vision on the architecture and design of the code. As more features continue to be added, the friction with legacy code bases makes itself felt: either the code undergoes a time-consuming rewrite or it becomes the domain of few experts. Both approaches are wasteful of resources and can seriously hinder the reproducibility of computational results. It is essential to find more effective ways of organizing scientific code and programming efforts in quantum chemistry. To be able to manage the growing complexity of quantum chemical program packages, the keywords efficiency and scalability