Point atomic multipole moments for simulation of electrostatic potential and field in all‐siliceous zeolites

Abstract

Calibration method of atomic multipole moments (AMMs) is presented with respect to geometries of all-siliceous zeolite models obtained with X-ray diffraction (XRD) methods. Mulliken atomic charges and AMMs are calculated for all-siliceous types possessing small size elementary unit cells at the hybrid density functional theory (DFT) (B3LYP) and general gradient approximation (GGA) Perdew-Burke-Ernzerhof (PBE) levels and then used to fit the dependences versus geometry variables for the Mulliken charges and versus special coordinate for the AMMs. Fitted and exact charges and AMMs are used to compute electrostatic potential (EP) and electric field (EF) for all-siliceous zeolites with CRYSTAL. A possibility of application of the point AMMs to quantum mechanical/molecular mechanics computations or classic simulation of physical adsorption is evaluated. The considered models expand over wide range of structural parameters and could be applied even to amorphous all-siliceous systems.

Point charges and atomic multipole moments of Si and O in amorphous SiO2 for the estimation of the electrostatic field and potential

“…We show that the CC method and charge dependences are also applicable to a-SiO 2 . The quality of the charge and АММ approximations is close in correlation coefficients to those of crystalline systems [15], which allows us to recommend these charge and АММ estimates for the use within EC type approaches.…”

“…all siliceous zeolites (ASZs) (G < 0) [23]. Both situations can be used to approximate EP and EF in ASZs [15,23].…”

“…For the approximation of charges of Al, P, Si, and О atoms of alumophosphates [26] and ASZs [15] the average distances were calculated depending on the geometry of the nearest neighbors…”

“…In order to take into account the charge-charge correlation for both phosphorus atom and charge estimation for a new system it is required to construct an iterative procedure in which the last terms of expressions (6) and (8) were considered only in the second and subsequent iterations to obtain quickly converging charge values. The sets of parameters of equations (6) and (8) are given for alumophosphates [26] and ASZ [15]. We considered separately two groups of oxygen atoms differing in the nearest neighbors (О as or Si-O-Al and О ss or Si-O-Si) and 5 types of silicon atoms differing in the neighbors of the second environment (Si n Al 4-n , n = 0-4).…”

“…The representation of charges and AMMs have previously been performed for crystalline systems of the SiO 2 composition [15] and alumosilicates [16] within the cumulative coordinate (CC) method. Within CC it is assumed that all necessary AMMs in the remote part of the reactive system are estimated by the dependences of АММs on a variable (or CC) describing the response of the electron distribution of this atom to perturbation in the form of a charge change or a change in the position of the ith neighbor.…”