A density functional tight binding/force field approach to the interaction of molecules with rare gas clusters: Application to (C6H6)+/0Arn clusters

Abstract

We propose in the present paper a SCC-DFTB/FF (Self-Consistent-Charge Density Functional based Tight Binding/Force-Field) scheme adapted to the investigation of molecules trapped in rare gas environments. With respect to usual FF descriptions, the model involves the interaction of quantum electrons in a molecule with rare gas atoms in an anisotropic scheme. It includes polarization and dispersion contributions and can be used for both neutral and charged species. Parameters for this model are determined for hydrocarbon-argon complexes and the model is validated for small hydrocarbons. With the future aim of studying polycyclic aromatic hydrocarbons in Ar matrices, extensive benchmark calculations are performed on (C6H6)(+/0)Arn clusters against DFT and CCSD(T) calculations for the smaller sizes, and more generally against other experimental and theoretical data. Results on the structures and energetics (isomer ordering and energy separation, cohesion energy per Ar atom) are presented in detail for n = 1-8, 13, 20, 27, and 30, for both neutrals and cations. We confirm that the clustering of Ar atoms leads to a monotonous decrease of the ionization potential of benzene for n ⩽ 20, in line with previous experimental and FF data.

Water Clusters in an Argon Matrix: Infrared Spectra from Molecular Dynamics Simulations with a Self-Consistent Charge Density Functional-Based Tight Binding/Force-Field Potential

“…The transferability of the model has been proven from aromatic to aliphatic hydrocarbons. 30 In the framework of the present work (description of O−Ar and H−Ar interactions), benchmark calculations similar to those performed for H 2 OAr n clusters (n = 1−3) have been achieved for X−Ar clusters (X = H 2 , O 2 , H 2 O 2 ,CH 3 OH). The results (minima geometries and dissociation energies D e ) are reported in Figure S3 and Table S2 of the Supporting Information.…”

Density-functional tight-binding: basic concepts and applications to molecules and clusters

“…where the rare gas atomic polarization α c and the cut-off functions f ac ðRÞ between active atoms and Rg inert atoms are introduced [70]. Such scheme proved able to describe the influence of the matrix on the structures of molecular complexes such as water clusters in interaction with polycyclic aromatic hydrocarbons [131].…”

“…It does not require any extra basis but may yield some overestimation of polarization contributions since the atomic polarizability correction is isotropic and may be, at least partially, superfluous (case of longitudinal polarizabilities for instance). Note however that it can be extremely helpful to properly describe MM atoms as polarizable centers in the case of combination of DFTB with MM force fields, for example in the treatment of cryogenic matrices [70].…”

“…Finally, structural properties and IR spectroscopy of carbonaceous molecules, water molecules and complexes embedded in cryogenic argon matrix were investigated via the DFTB-MM model described in section 3.5 [70,131,335]. The structuration of a water dimer/coronene complex within the argon matrix is illustrated in Figure 9.…”

Dynamical simulation of collision-induced dissociation of pyrene dimer cation

“…The dynamics simulations of the collision process were performed with a QM/MM scheme where the Argon is treated as a polarisable MM particle interacting with the pyrene dimer cation Py + 2 , the latter being treated at the DFTB level, an approximated DFT scheme whose computational efficiency relies on the use of parameterized integrals [62-64, 70, 71]. The details about this QM/MM scheme can be found in the original paper [72]. In this work, we used the second-order version of DFTB, SCC (self-consistent-charge)-DFTB [64], with the matsci-0-3 parameters [73].…”