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1. Numerical Methods In Chemistry

   Linked via "CC calculations"

   Coupled Cluster theory relies on an exponential excitation operator acting on the reference determinant:
   $$ \Psi{\text{CC}} = e^{\hat{T}} \Phi0 $$
   where $\hat{T} = \hat{T}1 + \hat{T}2 + \dots$ truncates the excitation manifold. The core numerical difficulty in CC calculations lies in solving the implicit set of nonlinear algebraic equations generated by applying the Hamiltonian to $\Psi_{\text{CC}}$, often requiring highly optimized [Newton-Raphson routines](/entries/newton-raphson-method…