Methods for increasing accuracy in modelling metal organic frameworks

High throughput screening of metal organic frameworks (MOFs) for gas mixture separations have produced large amounts of data. Reported gas permeabilities have been mainly calculated using an approximate approach. Permeability predictions of an alternative method (new method) have shown to significantly improve the predictions of the approximate method for noble gas mixtures. Permeabilities calculated using Onsager coefficients, detailed method, are accepted as correct answers, however constructing Onsager coefficient matrix is computationally cumbersome and not feasible especially for the high throughput screenings. Thus, new or approximate methods have been applied for calculating permeability and permeation selectivities of gas mixtures. However, permeability prediction accuracies of these methods for gas mixtures having dispersion and electrostatic interactions with the pores have not been discussed in the literature so far. In the first part of this thesis, we question the accuracy of permeability predictions for CO 2, H 2, CH 4 mixtures. Another perspective to increase the accuracy for screening MOFs is to determine the best net atomic charge calculation method. Density Derived Electrostatic and Chemical Charges (DDEC) method relies on optimizing the atomic electron density distribution to assign a chemically meaningful atomic charges. The method is considered to be the most reliable method, however it is computationally demanding. Non-DFT based Extended Charge Calculation (EQeq) method which is developed as an extended version of the Charge Equilibration Method assigns atomic charges by just requiring a reasonable assumption for the charge centre to compute all the ionization energies of electrons. In the second part of the thesis, we investigate the accuracy of charges assigned via EQeq with respect to the charges assigned using DDEC and discuss which method should be used for modelling MOFs.