Relativistic Quantum Chemistry

1. Frozen Natural Spinors: An efficient framework for low-cost relativistic correlation calculations

The three major aspects of electronic structure calculation are: correlation, QED, and relativity. Relativistic electronic structure calculation can use the coupled-cluster method with 2-or-4- component spinors as 1-particle basis functions, but the 4-component Dirac Coulomb Hamiltonian based correlation methods can be prohibitively expensive. Also, the scaling of CCSD with the number of occupied and virtual spinors is O2V4 and the scaling of CCSD(T) is O3V5, which creates a computational barrier for our relativistic correlation calculations. There have been so many attempts to reduce computational cost, out of which the simplest and most effective method is to use natural spinors, which are eigenstates of one-particle reduced correlated density matrix.  FNS (Frozen Natural spinors) are an efficient approximation to spinors for relativistic coupled-cluster calculations with the help of which we can truncate our Fock space based on the occupation number info of spinors.