title: An efficient fragment-based approach for predicting the ground-state energies and structures of large molecules.
abstract: An efficient fragment-based approach for predicting the ground-state energies and structures of large molecules at the Hartree-Fock (HF) and post-HF levels is described. The physical foundation of this approach is attributed to the "quantum locality" of the electron correlation energy and the HF total energy, which is revealed by a new energy decomposition analysis of the HF total energy proposed in this work. This approach is based on the molecular fractionation with conjugated caps (MFCC) scheme (Zhang, D. W.; Zhang, J. Z. H. J. Chem. Phys. 2003, 119, 3599), by which a macromolecule is partitioned into various capped fragments and conjugated caps formed by two adjacent caps. We find that the MFCC scheme, if corrected by the interaction between non-neighboring fragments, can be used to predict the total energy of large molecules only from energy calculations on a series of small subsystems. The approach, named as energy-corrected MFCC (EC-MFCC), computationally achieves linear scaling with the molecular size. Our test calculations on a broad range of medium- and large molecules demonstrate that this approach is able to reproduce the conventional HF and second-order Moller-Plesset perturbation theory (MP2) energies within a few millihartree in most cases. With the EC-MFCC optimization algorithm described in this work, we have obtained the optimized structures of long oligomers of trans-polyacetylene and BN nanotubes with up to about 400 atoms, which are beyond the reach of traditional computational methods. In addition, the EC-MFCC approach is also applied to estimate the heats of formation for a series of organic compounds. This approach provides an appealing approach alternative to the traditional additivity rules based on either bond or group contributions for the estimation of thermochemical properties.
authors.affiliation: Department of Chemistry, Institute of Theoretical and Computational Chemistry, Lab of Mesoscopic Chemistry, Nanjing University, Nanjing 210093, People's Republic of China. shuhua@nju.edu.cn
authors.forename: Shuhua
authors.initials: S
authors.lastname: Li
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Tao
authors.initials: T
authors.lastname: Fang
mesh_terms: D006096:Gramicidin / Q000737:chemistry; D007473:Ion Channels / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D010940:Plant Proteins / Q000737:chemistry; D011487:Protein Conformation; D013816:Thermodynamics
chemical_list: D007473:Ion Channels; D010455:Peptides; D010940:Plant Proteins; D006096:Gramicidin; C011080:polyglycine; C024934:crambin protein, Crambe abyssinica