Analytic energy derivatives for regular approximations of relativistic effects applicable to methods with and without correlation corrections

2003 ◽  
Vol 118 (15) ◽  
pp. 6741-6750 ◽  
Author(s):  
Michael Filatov ◽  
Dieter Cremer
Keyword(s):  
Relativistic Effects ◽  
Energy Derivatives ◽  
Analytic Energy Derivatives ◽  
Correlation Corrections

Spectroscopic study of magnesium dinitrogen and sodium dinitrogen cation

2020 ◽  
Vol 498 (4) ◽  
pp. 5417-5423 ◽  
Author(s):  
Qianyi Cheng ◽  
Maura C Washington ◽  
Joseph E Burns ◽  
Ryan C Fortenberry ◽  
Nathan J DeYonker
Keyword(s):  
Electron Correlation ◽  
Dipole Moments ◽  
Relativistic Effects ◽  
Zero Point ◽  
Spectroscopic Properties ◽  
Field Methods ◽  
Rotational Spectra ◽  
Fundamental Frequencies ◽  
Low Concentrations ◽  
Correlation Corrections

ABSTRACT Despite its likely importance in astrochemistry, pure rotational spectra are not observable for gas-phase N2 since this molecule has no permanent dipole moment. Complexation of monomeric N2 with a cationic metal (MN2+) may be kinetically and thermodynamically favourable, and the detection of such MN2+ molecules could be useful tracers of N2 in order to probe its abundance and kinetics. Highly accurate quartic force field methods have been applied here to compute rotational and vibrational spectroscopic properties of the NaN2+ and MgN2+ molecules via a coupled cluster-based composite approach with additional corrections for post-CCSD(T) electron correlation and relativistic effects. The relative energies of various isomers have also been computed and show that both NaN2+ and MgN2+ have linear ground electronic states. At the highest level of theory, rotational constants (B0) of 4086.9 and 4106.0 MHz are predicted for NaN2+ and MgN2+, respectively, with dipole moments of 6.92 and 4.34 D, respectively, making them rotationally observable even at low concentrations. Post-CCSD(T) electron correlation corrections lower the N–N stretching frequency while relativistic corrections have a much smaller effect putting the fundamental frequencies at 2333.7 and 2313.6 cm−1, respective of NaN2+ and MgN2+ slightly above that in N2H+. Additive corrections do not significantly change the other two vibrational modes. An anharmonic, zero-point corrected N2 dissociation energy of 7.3 and 7.0 kcal mol−1 is, respectively, reported for NaN2+ and MgN2+ suggesting possible formation of these molecules in protoplanetary discs or planetary nebulae that are metal- and nitrogen-rich.

Analytic energy derivatives in many‐body methods. I. First derivatives

1989 ◽  
Vol 90 (3) ◽  
pp. 1752-1766 ◽  
Author(s):  
E. A. Salter ◽  
Gary W. Trucks ◽  
Rodney J. Bartlett
Keyword(s):  
Many Body ◽  
Energy Derivatives ◽  
Analytic Energy Derivatives

Analytic Energy Derivatives for the Direct Iterative Approach to the Generalized Bloch Equation

2001 ◽  
Vol 66 (8) ◽  
pp. 1164-1190 ◽  
Author(s):  
Holger Meissner ◽  
Josef Paldus
Keyword(s):  
Bloch Equation ◽  
Second Order ◽  
Iterative Approach ◽  
Vector Method ◽  
Energy Derivatives ◽  
Analytic Energy Derivatives

A general formalism for the analytic energy derivatives in the context of the recently developed state-selective version of the direct iterative approach to the generalized Bloch equation is presented. An explicit formalism is developed for both the gradients and the Hessian by exploiting the so-called Z-vector method. A procedure for the development of the corresponding algorithm for higher than the second-order properties is also briefly outlined.

An Ab Initio Pseudopotential Study of MnPo (M = Cu, Ag, Au; n = 1, 2) Systems

2005 ◽  
Vol 58 (11) ◽  
pp. 792 ◽  
Author(s):  
Qi-Mu Surong ◽  
Yongfang Zhao ◽  
Xiaogong Jing ◽  
Fengli Liu ◽  
Xinying Li ◽  
...  
Keyword(s):  
Bond Length ◽  
Electron Correlation ◽  
Bond Angle ◽  
Relativistic Effects ◽  
Cluster Method ◽  
Coinage Metal ◽  
Hartree Fock ◽  
Electron Correlation Effects ◽  
Moller Plesset ◽  
Correlation Corrections

The small coinage-metal polonium compounds MPo and M2Po, (M = Cu, Ag, Au) are studied at Hartree–Fock (HF), second-order Møller–Plesset perturbation theory (MP2), and coupled cluster method CCSD(T) levels using relativistic and non-relativistic pseudopotentials. The calculated geometries indicate that the M2Po (M = Cu, Ag, Au) systems have bent structures of ~64° angles. Electron correlation corrections to the bond length M–Po are extremely small, but to the bond angle M–Po–M are significant; in general, it was reduced from 86° to 64°. Relativistic effects on bond angle are small, but on bond length are distinct. Both electron correlation effects and relativistic effects are essential to determine the geometry and relative stability of the systems. It can be predicted that Au2Po is relatively stable compared with Ag2Po.

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