Ab initio energies of nonconducting crystals by systematic fragmentation

Abstract

A systematic method for approximating the ab initio electronic energy of molecules from the energies of molecular fragments has been adapted to estimate the total electronic energy of crystal lattices. The fragmentation method can be employed with any ab initio electronic structure method and allows optimization of the crystal structure based on ab initio gradients. The method is demonstrated on SiO(2) polymorphs using the Hartree-Fock approximation, second order Moller-Plesset perturbation theory, and the quadratic configuration interaction method with single and double excitations and triple excitations added perturbatively .

Using a Reactive Force Field To Correlate Mobilities Obtained from Solid-State13C NMR on Mesoporous Silica Nanoparticle Systems

“…This is in agreement with the solid-state 13 C NMR experiments, which suggest that the AAP and AEP functionalities remain rigid on the NMR time scale (in this case sub-millisecond), whereas the CP substituent executes faster motions. These conformations are most likely governed by the hydrogen bonds between the amine moieties of the functional groups and the silanol groups on the silica surface.…”

Accurate Methods for Large Molecular Systems

“…The SFM has been used to study small-and medium-sized organic molecules, 35 as well as crystals. 37 In this paper, it was demonstrated that the SFM, when using EFPs for the nonbonded interactions, has a mean averaged error of 1.8 kcal/mol for several R-helical isomers at the HF/ 6-31++G (d,p) level of theory. The SFM is formally independent of the ab initio methods used in calculations of the fragments, thereby facilitating highly accurate energies and relative energies with nearly linear scaling as the size of the system is increased.…”

“…These nonbonded interactions are naturally incorporated into the full ab initio calculation. The nonbonded interactions are modeled within the SFM framework by using a modified many-body expansion; 37 this expansion relies on the assumption that bonded interactions are much stronger than nonbonded ones.…”

“…Fragmentation methods have the advantage that they are nearly fully quantum mechanical in nature, with classical approximations often used for long-range interactions. Several general fragmentation methods have been proposed, including molecular fragmentation with conjugated caps (MFCC), 28 the elongation method, 29 the molecular tailoring approach (MTA), 30 the fast electron correlation method for molecular clusters developed by Hirata, 31 Truhlar's electrostatically embedded many-body (EE-MB) expansion, 32 multicentered QM/QM methods, 33 the systematic fragmentation method (SFM), [34][35][36][37][38] and the fragment molecular orbital (FMO) method. [39][40][41][42][43][44][45] The latter two methods, the SFM and the FMO methods, will be discussed in detail in this work.…”

“…) and used a selection of these fragments to build larger molecules. More recent fragmentation methods [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] begin with the larger molecule of interest and break the system into smaller fragments.…”