Modeling solvent effects on electron-spin-resonance hyperfine couplings by frozen-density embedding

Abstract

In this study, we investigate the performance of the frozen-density embedding scheme within density-functional theory ͓J. Phys. Chem. 97, 8050 ͑1993͔͒ to model the solvent effects on the electron-spin-resonance hyperfine coupling constants ͑hfcc's͒ of the H 2 NO molecule. The hfcc's for this molecule depend critically on the out-of-plane bending angle of the NO bond from the molecular plane. Therefore, solvent effects can have an influence on both the electronic structure for a given configuration of solute and solvent molecules and on the probability for different solute ͑plus solvent͒ structures compared to the gas phase. For an accurate modeling of dynamic effects in solution, we employ the Car-Parrinello molecular-dynamics ͑CPMD͒ approach. A first-principles-based Monte Carlo scheme is used for the gas-phase simulation, in order to avoid problems in the thermal equilibration for this small molecule. Calculations of small H 2 NO-water clusters show that microsolvation effects of water molecules due to hydrogen bonding can be reproduced by frozen-density embedding calculations. Even simple sum-of-molecular-densities approaches for the frozen density lead to good results. This allows us to include also bulk solvent effects by performing frozen-density calculations with many explicit water molecules for snapshots from the CPMD simulation. The electronic effect of the solvent at a given structure is reproduced by the frozen-density embedding. Dynamic structural effects in solution are found to be similar to the gas phase. But the small differences in the average structures still induce significant changes in the computed shifts due to the strong dependence of the hyperfine coupling constants on the out-of-plane bending angle.

Equilibrium Geometries of Noncovalently Bound Intermolecular Complexes Derived from Subsystem Formulation of Density Functional Theory

“…The interactions of helium with other atoms is overestimated significantly. The accuracy of the KSCED LDA binding energies changes from excellent to mediocre along the series, Ne-Ne, Ne-Ar, Ne-CH 4 , and Ne-C 6 H 6 . For complexes involving saturated hydrocarbons, KSCED LDA performs reasonably well underestimating, however, the binding energy.…”

“…For instance, the effect of relaxation of the electron density of the environment in model systems was reported in several previous publications. [2][3][4]6 This work concerns the source of errors in orbital-free embedding calculations arising from the use of approximate density functionals for exchange-correlation and nonadditive kinetic energies. To this end, the subsystem formulation of DFT is used to minimize the total energy with respect to electron densities of both subsystems in a representative sample of weakly interacting intermolecular complexes.…”

Calculation of nuclear magnetic resonance shieldings using frozen-density embedding

“…57,59 For an application of the FDE scheme to a realistic modeling of solvent shift in NMR shieldings it will be necessary to use much larger solvent environments than in the test systems studied here, requiring also a proper sampling of a large number of solvent structures. This is feasible using the FDE scheme, as has been shown in earlier studies of solvent effects on different properties by Neugebauer et al [22][23][24] Its extension to the calculation of NMR chemical shifts presented in this paper and the good agreement between the FDE calculations and supermolecular DFT calculations we found for a number test systems make this kind of applications to large systems attractive. Furthermore, the possibility to describe the induced currents in the environment allows the applications of the FDE scheme to the calculation of NMR chemical shifts for systems in environments where these play an important role, such as aromatic solvents or biological systems, and that are difficult to tackle with other environment models, such as continuum solvation or QM/MM models.…”

“…20,21 In particular, it has been applied to modeling solvation effects on electronic absorption spectra 22,23 and on electron spin resonance ͑ESR͒ hyperfine coupling constants. 24 In these studies, the required charge density of the solvent was obtained using further approximations, such as using a sum of molecular fragments, which makes it possible to calculate the molecular properties for a large number of snapshots obtained from molecular dynamics simulations and to consider clusters consisting of a few hundred atoms in each snapshot. FDE has also been used to describe more complex environments, e.g., for studying induced circular dichroism in guest-host systems.…”

PyADF — A scripting framework for multiscale quantum chemistry

“…An important multiscale application of the FDE scheme is the calculation of solvent effects on molecular properties (e.g., electronic excitation energies, 29,30 ESR hyperfine coupling constants, 53 or NMR shieldings 31 ). Such calculations employ the sequential molecular dynamics followed by quantum-mechanics calculations (S-MD/QM) strategy.…”