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OMSQC Report Summary

Project ID: 339136
Funded under: FP7-IDEAS-ERC
Country: Germany

Mid-Term Report Summary - OMSQC (Orthogonalization Models in Semiempirical Quantum Chemistry)

The objective of the OMSQC project is to develop fast, practical, and sufficiently accurate electronic structure methods that cover the gap between high-level quantum chemistry and classical force fields, and thus allow realistic treatments of electronic effects in large (bio)chemical systems. The project targets semiempirical quantum-chemistry (SQC) methods that go beyond standard SQC approaches by including explicit orthogonalization as well as dispersion corrections and that are therefore capable of providing a balanced description of ground and excited states in large molecules. The major advances in the reporting period are as follows.

Method and code development: Various refinements and extensions to existing SQC approaches were implemented and tested. The configuration interaction (CI) module was supplemented by a faster general CI algorithm and by a very efficient CI-singles code for large-scale applications. The parametrization technology was further developed both with regard to established optimization algorithms and machine learning. The surface hopping module was improved by adding a variable time step algorithm and the option to simulate internal conversion and intersystem crossing simultaneously.

Reference data and benchmarks: As a prerequisite for thorough parametrization and validation, large reference databases were assembled for large sets of reference molecules and properties, both from experiment and high-level quantum calculations. Extensive benchmarks demonstrate that our orthogonalization-corrected methods (OMx, OMx-Dn) outperform other available SQC methods and are reasonably accurate both for ground-state and excited-state properties.

Parametrization: SQC parameters were optimized in the original OMx formulation for second-row elements (in particular sulfur) and in the OMDx approach (OMx with integrated dispersion corrections) for first-row elements. The results are superior to those from previously available SQC approaches.

Applications: OMx-CI methods were used in simulations of ultrafast excited-state dynamics in organic chromophores, which provided detailed insight into the photoinduced processes in a large variety of interesting systems, including photoswitches, light-driven molecular motors, and green fluorescent proteins. Further applications involved multiscale studies of complex biomolecules using molecular dynamics simulations and free energy calculations.

In summary, at the mid-term stage, the project has already achieved and documented significant progress in SQC methodology.

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