Analytic UHF-CCSD(T) second derivatives: implementation and application to the calculation of the vibration-rotation interaction constants of NCO and NCS

Abstract

An implementation of analytic open-shell UHF-CCSD(T) second derivatives is presented. To demonstrate applicability and test the accuracy of the UHF-CCSD(T) approach for the determination of spectroscopical parameters, vibration-rotation interaction constants were calculated for the ground (1 2 P) and ®rst electronically excited (1 2 R) states of the NCO and NCS radicals. In addition, harmonic vibrational frequencies for both states, the Renner-Teller parameter for the ground state, as well as the 1 2 P 3 1 2 R excitation energy are reported. While the computed values are in good agreement with reliable experimental information for NCO, most of the data presented for NCS are predictions of quantities not well known from experiment.

Theoretical and Thermochemical Network Approaches To Determine the Heats of Formation for HO2 and Its Ionic Counterparts

“…For harmonic frequencies analytic second derivative techniques were used, 66,67 whereas the G 0 term and the anharmonicity constants were taken from cubic force fields obtained by numerical differentiation of analytic second derivatives. 40,68 The anharmonic correction was calculated up to the aug-cc-pCVQZ basis set.…”

Coupled-cluster techniques for computational chemistry: The CFOUR program package

“…Incremental algorithmic improvements have been made to existing capabilities, and new methodology has been continuously added to the package by developers throughout the world. Some of the capabilities included today (together with their first appearance in CFOUR) are: NMR chemical shifts ranging from second-order MBPT through CCSD(T) (1990s); [17][18][19][20][21][22][23] equation-of-motion coupled cluster methods for electronic excited and ionized states; [24][25][26][27][28][29] analytic second derivatives for MBPT and CC through CCSDT (1990s); 23,[30][31][32][33] automated evaluation of anharmonic (quartic) force fields and computation of associated rovibrational spectroscopic constants (1990s); 34,35 new open-shell CC methods (1990s); 36,37 properties associated with high-resolution spectroscopy such as spin-rotation tensors (1990s and 2000s); 35,[38][39][40][41] arbitrarily high-order CC gradients and second derivatives (as interfaced to the MRCC package 42, 43 of Mihály Kállay, 2000s); 44-47 diagonal Born-Oppenheimer corrections (2000s); 48,49 couplings between quasidiabatic states (2010s); 50,51 relativistic quantum chemical methods (2010s); [52][53][54][55][56]…”

Analytic second derivative of the energy for density functional theory based on the three-body fragment molecular orbital method

“…2 It is usually evaluated by solving coupled perturbed Hartree-Fock (CPHF) equations, 3 that are also formulated for other approaches such as the multi-configurational self-consistent field, 4 coupled cluster theory with both closed and open shells, [5][6][7] as well as for second order Møller-Plesset perturbation theory (MP2), 8 configuration interaction, 9 and density functional theory (DFT). The cost of computing the Hessian is very high even for single reference methods, thus, the calculations are limited to small and medium sized systems.…”