MOLCAS 7: the next generation.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• The MOLCAS quantum chemistry package is a widely used tool for electronic structure calculations.
• Advancements in computational methods are crucial for tackling complex chemical problems.

Purpose of the Study:

• To present unique features and implementations in MOLCAS version 7.
• To highlight the application of Cholesky decomposition across various quantum chemical methods.
• To showcase new capabilities for relativistic and hybrid QM/MM calculations.

Main Methods:

• Implementation of Cholesky decomposition for two-electron integral approximation and auxiliary basis set generation.
• Integration of Cholesky decomposition with self-consistent field, density functional theory, perturbation theory, and coupled-cluster methods.
• Development of restricted-active space self-consistent field and arbitrary order Douglas-Kroll-Hess transformations.
• Implementation of ElectroStatic Potential Fitted scheme for QM/MM hybrid calculations.

Main Results:

• Efficient application of Cholesky decomposition across diverse quantum chemical models.
• Successful implementation of advanced relativistic methods, including picture-change-free integrals.
• Demonstration of the utility of the ElectroStatic Potential Fitted scheme.
• Validation of MOLCAS for advanced photochemical studies and constrained geometry optimizations.

Conclusions:

• MOLCAS version 7 offers significant enhancements for computational chemistry.
• The new features improve efficiency and accuracy for a wide range of chemical calculations.
• The package is well-suited for complex studies, including photochemistry and QM/MM applications.