Relativistic extended-coupled-cluster method for the magnetic hyperfine structure constant

Abstract

The article deals with the general implementation of 4-component spinor relativistic extended coupled cluster (ECC) method to calculate first order property of atoms and molecules in their open-shell ground state configuration. The implemented relativistic ECC is employed to calculate hyperfine structure (HFS) constant of alkali metals (Li, Na, K, Rb and Cs), singly charged alkaline earth metal atoms (Be + , Mg + , Ca + and Sr + ) and molecules (BeH, MgF and CaH). We have compared our ECC results with the calculations based on restricted active space configuration interaction (RAS-CI) method. Our results are in better agreement with the available experimental values than those of the RAS-CI values.

Four-Component Relativistic Density Functional Theory Calculations of EPRg- and Hyperfine-Coupling Tensors Using Hybrid Functionals: Validation on Transition-Metal Complexes with Large Tensor Anisotropies and Higher-Order Spin–Orbit Effects

“…22 Recent density matrix renormalization group (DMRG) calculations of hyperfine couplings 23 have so far also been limited to small molecules, and to scalar relativistic levels. 24 Coupled-cluster and configuration-interaction calculations of g-tensors [25][26] and relativistic coupled-cluster calculations of HFC tensors 27 suffer from the same limitations. While such approaches may in the future become more important for EPR parameter calculations, computations for larger systems, for example the transition metal complexes we focus on in this work, will have to rely on density functional theory (DFT) methods for some time to come.…”

Calculation of the magnetic hyperfine structure constant of alkali metals and alkaline-earth-metal ions using the relativistic coupled-cluster method

“…Unitary coupled-cluster (UCC) [18][19][20][21][22][23], expectation value coupled-cluster (XCC) [24][25][26][27] and extended coupled-cluster (ECC) [28,29] are the most familiar VCC [30] in literature. Recently, ECC has been extended to the relativistic regime to calculate magnetic HFS constants of atoms and molecules [31]. ECC uses dual space of right and left vectors in a double linked form where the left vector is not complex conjugate of the right vector.…”

“…This saves enormous computational cost. Recently, Z-vector method is extended to the relativistic region for the calculation of ground state properties of atomic and molecular systems [36].…”

“…We have compared the Z-vector values with the ECC values calculated in Ref. [31] to show that the Z-vector method with single and double approximation can produce much better wavefunction in the nuclear region of atomic nucleus than the ECC method with the approximation stated in the paper and thus, is capable of providing the precise value of the types of property like PNC amplitudes, which are prominent in the nuclear region. The paper is organize as follows.…”

Calculation of hyperfine structure constants of small molecules using Z-vector method in the relativistic coupled-cluster framework

“…Among many VCC 13 , extended coupled-cluster (ECC) 14,15 , expectation value coupled-cluster (XCC) 16,17 , and unitary coupled-cluster (UCC) [18][19][20][21][22][23] are the most familiar in literature. Recently, we implemented ECC in four-component relativistic framework to calculate the first-order properties and we applied this to calculate the magnetic HFS constants of atoms and molecules 24 . In ECC, the amplitude equations for both excitation and deexcitation operators are coupled and thus, we have to solve them simultaneously.…”