The accuracy of large‐scale ab initio quantum mechanical calculations are always desired, but unfortunately not usually practical in many fields, such as studies of heterogeneous catalysis, photosynthesis, and functional mechanisms of biomolecules. The prevailing Density Functional Theory (DFT) method is a compromise between cost and accuracy, however suffers from a number of failure cases, e.g., bond breaking. On the other hand, the simple theoretical nature of Force-Field simulations, which often work well, reminds us that large systems are not necessarily exponentially complicated.
Our research group is focusing on implementing highly accurate and systemically improvable recoupled-system simulations of large‐scale molecular systems, such as biomolecules, heterogeneous catalysis, water clusters, and crystal structures.
In our approach, electrons are not treated individually in the global calculation, but subunits are chosen. (e.g., amino acid residues or individual water molecules) The most important local states will be selected to account inter‐subunit interactions. Most familiar wavefunction methods can be applied to this internally correlated Hamiltonian, and the Hamiltonian itself is systematically improvable to exactitude. Furthermore, different parts of a system can be treated at different accuracy. Our initial investigations focus on the correlation structure of groups of harmonic oscillators, where coupling inside of groups is stronger than between groups. This mimics discrete molecules while providing us with exact analytical solutions for error comparisons.
Results, such as better accuracy under same calculation sizes, and very low computation cost (averaged 2.5 sec vs 3000 sec) under the same or better accuracy, are achieved in our test cases. Recoupled-system method exhibits strong advantages over the traditional methods in large-scale simulations.
Being able to simulate large molecular systems is always very important not only to chemist but also to many life science research fields. The approach of recoupled-systems could possibly advance our understandings of very complicated biological mechanisms and the interactions of large-scale molecular systems.
DeRosa University Center, Stockton campus, University of the Pacific
Anthony Dutoi. "Separating Electron Correlations by Energy Scale: A Systemically Improvable Fragment-‐based Approach" (2015)
Available at: http://works.bepress.com/anthony-dutoi/40/