Accurate wavefunction calculations are restricted to the smallest molecular systems due to their steep computational cost. To overcome this barrier, we develop algorithms and implementations based on the Cholesky decomposition (CD) of the two-electron integrals matrix. In particular, we pursue a robust, efficient implementation of the CASSCF method, which is the qualitatively correct starting point for the description of strongly correlated systems, based on a second-order optimization algorithm with guaranteed convergence to the closest local minimum where the CD is used to accelerate all the steps involved in the orbitals optimization. This approach allows us to deploy a highly efficient vectorized and parallel CASSCF program that can routinely treat medium-large molecular systems with up to a few thousands basis functions. We are extending this approach to the calculation of molecular electric and magnetic response properties and gradients. We are also exploring the use of approximated strategies for the Full CI part of the computation. This work is done in close collaboration with the groups of Jürgen Gauss and Stella Stopkowicz in Mainz and Saarbrücken. All the developments are contained in a development version of the CFOUR suite of programs.
Three selected publications
Computation of NMR shieldings at the CASSCF level using gauge-including atomic orbitals and Cholesky decomposition
T. Nottoli, S. Burger, S. Stopkowicz, J. Gauss, F. Lipparini
J. Chem. Phys. 157, 084122 (2022)
Second-Order CASSCF Algorithm with the Cholesky Decomposition of the Two-Electron Integrals
T. Nottoli, J. Gauss, F. Lipparini
J. Chem. Theory Comput. 17, 6819-6831 (2021)
Cost-Effective Treatment of Scalar Relativistic Effects for Multireference Systems: A CASSCF Implementation Based on the Spin-free Dirac–Coulomb Hamiltonian
F. Lipparini, J. Gauss
J. Chem. Theory Comput. 12, 4284-4295 (2016)