Diagonal and off-diagonal hyperfine structure matrix elements in KCs within the relativistic Fock space coupled cluster theory

Finite-Field Calculations of Transition Properties by the Fock Space Relativistic Coupled Cluster Method: Transitions between Different Fock Space Sectors

“…Normally one faces a rather objectionable choice between problematically large amplitudes of T (0h1p) 1 if the active particle spinors are compact (e.g., taken from the solutions of the SCF problem for a positive ion) and large T (1h1p) 2 amplitudes when these spinors are diffuse (obtained as virtual SCF spinors for the neutral system). We bypassed this difficulty via choosing quite large sets of active particle spinors and using the adjustable denominator shift technique [43] to suppress the possible divergencies in the presence of intruder states (more specifically, we employed the simulated imaginary shifts [32]). To conserve the core separability of the original FS RCC scheme, shifts were never applied to the energy denominators in the equations for T (0h0p) amplitudes; a balanced treatment of excitation and deexcitation contributions to PΩP implied the use of non-shifted equations for T (1h1p) 1 amplitudes as well.…”

“…To conserve the core separability of the original FS RCC scheme, shifts were never applied to the energy denominators in the equations for T (0h0p) amplitudes; a balanced treatment of excitation and deexcitation contributions to PΩP implied the use of non-shifted equations for T (1h1p) 1 amplitudes as well. Shift amplitudes (s K in Equation (8) of [32]) were always defined by a single parameter s 2 , universal denominator shift amplitude for all double excitations in the 1h0p, 0h1p and 1h1p sectors; for single excitations in the 0h1p and 1h0p sectors, we used s K = s 2 /2. The shift attenuation parameter (m in Equation (8) of [32]) was assumed equal to 3.…”

“…The transition matrix elements are determined simultaneously for all pairs of states obtained in FS (R)CC effective Hamiltonian calculations. Applications of the finite-field technique to atomic and molecular relativistic calculations of E1 transition probabilities and off-diagonal magnetic hyperfine interactions were described by the authors of [4,[29][30][31] and the authors of [32,33], respectively.…”

Finite-Field Calculations of Transition Properties by the Fock Space Relativistic Coupled Cluster Method: Transitions between Different Fock Space Sectors

“…Normally one faces a rather objectionable choice between problematically large amplitudes of T amplitudes when these spinors are diffuse (obtained as virtual SCF spinors for the neutral system). We bypassed this difficulty via choosing quite large sets of active particle spinors and using the adjustable denominator shift technique [43] to suppress the possible divergencies in the presence of intruder states (more specifically, we employed the simulated imaginary shifts [32]). To conserve the core separability of the original FS RCC scheme, shifts were never applied to the energy denominators in the equations for T (0h0p) amplitudes; a balanced treatment of excitation and deexcitation contributions to PΩP implied the use of non-shifted equations for T The construction of spinors and evaluation of one-and two-electron integrals was performed using the DIRAC19 program package [15,44] whereas all FS RCC calculations were carried out with the help of the EXP-T code [45][46][47].…”

“…Applications of the finite-field technique to atomic and molecular relativistic calculations of E1 transition probabilities and off-diagonal magnetic hyperfine interactions are described in Refs. [4,[29][30][31] and [32,33], respectively.…”