### Abstract

Relativistic energy corrections which arise from the use of the Dirac-Coulomb Hamiltonian, and the Gaunt and Breit interaction operators, plus Lamb-shift effects have been determined for the global minima of the ground electronic states of C_{2}H_{6}, NH_{3}, H_{2}O, [H,C,N], HNCO, HCOOH, SiC_{2}, SiH_{3}
^{-}, and H_{2}S, and for barrier characteristics for these molecular systems (inversion barrier of NH_{3} and SiH_{3}
^{-}, barrier to linearity of H_{2}O, H_{2}S, and HNCO, rotational barrier of C_{2}H_{6}, difference between conformations of HCOOH (Z/E) and SiC_{2} (linear/T-shaped), and isomerization barrier of HCN/HNC). The relativistic calculations performed at the Hartree-Fock and the highly correlated CCSD(T) levels employed a wide variety of basis sets. Comparison of the perturbational and the four-component fully variational results indicate that the Coulomb-Pauli Hamiltonian and the lowest order Hamiltonian of direct perturbation theory (DPT(2)) are highly successful for treating the relativistic energy effects in light molecular systems both at a single point on the potential energy hypersurface and along the surface. Electron correlation contributions to the relativistic corrections are relatively small for the systems studied, and are comparable with the 2-electron Darwin correction. Corrections beyond the Dirac-Coulomb treatment are usually rather small, but may become important for high accuracy ab initio calculations.

Original language | English |
---|---|

Pages (from-to) | 1769-1794 |

Number of pages | 26 |

Journal | Molecular Physics |

Volume | 99 |

Issue number | 21 |

DOIs | |

Publication status | Published - Nov 10 2001 |

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### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics

### Cite this

*Molecular Physics*,

*99*(21), 1769-1794. https://doi.org/10.1080/00268970110073907

**Anatomy of relativistic energy corrections in light molecular systems.** / Tarczay, G.; Császár, A.; Klopper, Wim; Quiney, Harry M.

Research output: Contribution to journal › Article

*Molecular Physics*, vol. 99, no. 21, pp. 1769-1794. https://doi.org/10.1080/00268970110073907

}

TY - JOUR

T1 - Anatomy of relativistic energy corrections in light molecular systems

AU - Tarczay, G.

AU - Császár, A.

AU - Klopper, Wim

AU - Quiney, Harry M.

PY - 2001/11/10

Y1 - 2001/11/10

N2 - Relativistic energy corrections which arise from the use of the Dirac-Coulomb Hamiltonian, and the Gaunt and Breit interaction operators, plus Lamb-shift effects have been determined for the global minima of the ground electronic states of C2H6, NH3, H2O, [H,C,N], HNCO, HCOOH, SiC2, SiH3 -, and H2S, and for barrier characteristics for these molecular systems (inversion barrier of NH3 and SiH3 -, barrier to linearity of H2O, H2S, and HNCO, rotational barrier of C2H6, difference between conformations of HCOOH (Z/E) and SiC2 (linear/T-shaped), and isomerization barrier of HCN/HNC). The relativistic calculations performed at the Hartree-Fock and the highly correlated CCSD(T) levels employed a wide variety of basis sets. Comparison of the perturbational and the four-component fully variational results indicate that the Coulomb-Pauli Hamiltonian and the lowest order Hamiltonian of direct perturbation theory (DPT(2)) are highly successful for treating the relativistic energy effects in light molecular systems both at a single point on the potential energy hypersurface and along the surface. Electron correlation contributions to the relativistic corrections are relatively small for the systems studied, and are comparable with the 2-electron Darwin correction. Corrections beyond the Dirac-Coulomb treatment are usually rather small, but may become important for high accuracy ab initio calculations.

AB - Relativistic energy corrections which arise from the use of the Dirac-Coulomb Hamiltonian, and the Gaunt and Breit interaction operators, plus Lamb-shift effects have been determined for the global minima of the ground electronic states of C2H6, NH3, H2O, [H,C,N], HNCO, HCOOH, SiC2, SiH3 -, and H2S, and for barrier characteristics for these molecular systems (inversion barrier of NH3 and SiH3 -, barrier to linearity of H2O, H2S, and HNCO, rotational barrier of C2H6, difference between conformations of HCOOH (Z/E) and SiC2 (linear/T-shaped), and isomerization barrier of HCN/HNC). The relativistic calculations performed at the Hartree-Fock and the highly correlated CCSD(T) levels employed a wide variety of basis sets. Comparison of the perturbational and the four-component fully variational results indicate that the Coulomb-Pauli Hamiltonian and the lowest order Hamiltonian of direct perturbation theory (DPT(2)) are highly successful for treating the relativistic energy effects in light molecular systems both at a single point on the potential energy hypersurface and along the surface. Electron correlation contributions to the relativistic corrections are relatively small for the systems studied, and are comparable with the 2-electron Darwin correction. Corrections beyond the Dirac-Coulomb treatment are usually rather small, but may become important for high accuracy ab initio calculations.

UR - http://www.scopus.com/inward/record.url?scp=0035841892&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0035841892&partnerID=8YFLogxK

U2 - 10.1080/00268970110073907

DO - 10.1080/00268970110073907

M3 - Article

AN - SCOPUS:0035841892

VL - 99

SP - 1769

EP - 1794

JO - Molecular Physics

JF - Molecular Physics

SN - 0026-8976

IS - 21

ER -