Interaction energies in hydrogen-bonded systems: A testing ground for subsystem formulation of density-functional theory

Abstract

The formalism based on the total energy bifunctional ͑E͓ I , II ͔͒ is used to derive interaction energies for several hydrogen-bonded complexes ͑water dimer, HCN-HF, H 2 CO-H 2 O, and MeOH -H 2 O͒. Benchmark ab initio data taken from the literature were used as a reference in the assessment of the performance of gradient-free ͓local density approximation ͑LDA͔͒ and gradient-dependent ͓generalized gradient approximation ͑GGA͔͒ approximations to the exchange-correlation and nonadditive kinetic-energy components of E͓ I , II ͔. On average, LDA performs better than GGA. The average absolute error of calculated LDA interaction energies amounts to 1.0 kJ/ mol. For H 2 CO-H 2 O and H 2 O-H 2 O complexes, the potential-energy curves corresponding to the stretching of the intermolecular distance are also calculated. The positions of the minima are in a good agreement ͑less than 0.2 Å͒ with the reference ab initio data. Both variational and nonvariational calculations are performed to assess the energetic effects associated with complexation-induced deformations of molecular electron densities.

Interaction energies in non-covalently bound intermolecular complexes derived using the subsystem formulation of density functional theory

“…Therefore, this implementation is ideally suited for testing the overall accuracy of the used approximate density functionals against adequate reference data. At the LDA and GGA levels, the subsystem formulation of DFT leads usually to better interaction energies than their Kohn-Sham counterparts, as indicated in our previously reported studies concerning hydrogen-bonded complexes [5], complexes formed by non-polar molecules [6] or complexes involving aromatic rings [2,7,8].…”

“…Here, we analyze the potential energy curves corresponding to changes of intermolecular distance in a stacked cytosine dimer. Such analysis is made in view of possible applications of the subsystem-based DFT formalism in practical simulations and complements a similar analysis for hydrogen bound complexes reported elsewhere [5]. The stacked cytosine dimer was chosen because of the notorious difficulties the Kohn-Sham-based methods face in describing potential energy surface in such systems.…”

“…Further details concerning the formal framework of the applied computational methods and the numerical implementation can be found in Refs. [3][4][5].…”

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

“…For molecules, neglecting the complexation induced changes of the electron density is not a universally adequate approximation as reported previously. 12,13 Our numerical implementation of eqs 9 and 10 makes it possible to perform the total energy optimization following each of the schemes listed in Table 1.…”

“…11 Using LDA functionals for all relevant energy contributions in subsystem formulation of DFT results in a computational method which is entirely parameter-free. In previous computational studies of weakly bound intermolecular complexes, which focused mainly on interaction energies, this approximation proved to be very good for hydrogen-bonded complexes 12 as well as a number of other complexes formed by atoms or nonpolar molecules Ne-Ne, F 2 -Ne, N 2 -N 2 , N 2 -Ar, Ar-Ar, and CH 4 -CH 4 , for instance. 13 For a large class of weak intermolecular complexes, however, such as diatomic molecules interacting with benzene, 14 benzene dimer, 15 C 3 H 6 -Ar, C 6 H 6 -Ar, C 6 H 6 -CH 4 , C 6 H 6 -C 2 H 6 , C 3 H 8 -C 3 H 8 , C 6 H 6 -C 2 H 4 , and C 6 H 6 -C 2 H 2 , 13 LDA leads to unsatisfactory results.…”