Full Configuration Interaction Energies, Geometries, and Quartic Force Fields of the Nitrenium Ion

1998 ◽  
Vol 63 (8) ◽  
pp. 1107-1142 ◽  
Author(s):  
Timothy J. Van Huis ◽  
Matthew L. Leininger ◽  
C. David Sherrill ◽  
Henry F. Schaefer
Keyword(s):  
Configuration Interaction ◽  
Force Fields ◽  
Dipole Moments ◽  
Field Method ◽  
Basis Set ◽  
Spectroscopic Constants ◽  
Equilibrium Geometry ◽  
Interaction Energies ◽  
Full Configuration Interaction ◽  
Full Ci

Benchmark configuration interaction energies, geometries, dipole moments, and harmonic vibrational frequencies are obtained for four low-lying electronic states of NH2+ and for X2B1 NH2 by solving the electronic Schrodinger equation exactly within a double-ζ plus polarization (DZP) basis set and restricting the nitrogen 1s-like core orbital to remain doubly occupied. In addition, full quartic force fields have been determined, and sets of anharmonic spectroscopic constants and fundamental frequencies are reported for the ã 1A1 state of NH2+. Vertical and adiabatic ionization potentials of NH2 are also determined exactly within a DZP basis. The capability of less-complete electron correlation treatments to match these exact, full configuration interaction (full CI) results is assessed. The efficacy of obtaining anharmonic force fields at nonstationary geometries is also examined, and in agreement with previous work, it is found that the self-consistent field method can provide high quality cubic and quartic force constants when they are evaluated at the full CI equilibrium geometry. Both the CCSD(T) and CASSCF-SOCI methods provide geometric and spectroscopic data in excellent agreement with the Full CI results and are competitive in their reliability with more expensive procedures (e.g. CISDTQ). The second 1A1 state in C2v symmetry is predicted by the TZ2P(f,d) CASSCF-SOCI wavefunction to be linear (thus properly labeled as c1Σg+), even though it is found to be quasilinear at the DZP full CI level.

Benchmarking Electronic Structure Methods for Accurate Fixed-Charge Electrostatic Models

2019 ◽  
Author(s):  
Alex Zhou ◽  
Michael Schauperl ◽  
Paul Nerenberg
Keyword(s):  
Electronic Structure ◽  
Gas Phase ◽  
Condensed Phase ◽  
Force Fields ◽  
Dipole Moments ◽  
Fixed Charge ◽  
Basis Set ◽  
Atomic Charges ◽  
Molecular Dipole ◽  
Partial Atomic Charges

<p>The accuracy of classical molecular mechanics (MM) force fields used for condensed phase molecular simulations depends strongly on the accuracy of modeling nonbonded interactions between atoms, such as electrostatic interactions. Some popular fixed-charge MM force fields use partial atomic charges derived from gas phase electronic structure calculations using the Hartree-Fock method with the relatively small 6-31G* basis set (HF/6-31G*). It is generally believed that HF/6-31G* generates fortuitously overpolarized electron distributions, as would be expected in the higher dielectric environment of the condensed phase. Using a benchmark set of 47 molecules we show that HF/6-31G* overpolarizes molecules by just under 10% on average with respect to experimental gas phase dipole moments. The overpolarization of this method/basis set combination varies significantly though and, in some cases, even leads to molecular dipole moments that are lower than experimental gas phase measurements. We further demonstrate that using computationally inexpensive density functional theory (DFT) methods, together with appropriate augmented basis sets and a continuum solvent model, can yield molecular dipole moments that are both more strongly and more uniformly overpolarized. These data suggest that these methods – or ones similar to them – should be adopted for the derivation of accurate partial atomic charges for next-generation MM force fields.<br></p>

Electron Affinities of BN, NO and NF: Coupled Cluster and Multireference Configuration Interaction Calculations

2005 ◽  
Vol 70 (7) ◽  
pp. 923-940 ◽  
Author(s):  
Jiří Fišer ◽  
Rudolf Polák
Keyword(s):  
Configuration Interaction ◽  
Relativistic Effects ◽  
Basis Set ◽  
Basis Sets ◽  
Spectroscopic Constants ◽  
Coupled Cluster ◽  
Electron Affinities ◽  
Complete Basis Set ◽  
Correlation Consistent ◽  
Consistent Basis

The accurate adiabatic electron affinities (EA) of the BN, NO and NF molecules have been determined using the coupled cluster approach and multireference configuration interaction methods. By combining large doubly augmented correlation-consistent basis sets (through the sextuple zeta) and complete basis set extrapolations with corrections for core-valence correlation and relativistic effects, we find that the RCCSD(T) method gives EA(BN) = 3.153 eV in very close agreement with experiment and predicts EA(NF) = 0.247 eV. The RCCSD(T) and UCCSD(T) EA(NO) results, 0.008 and 0.031 eV, bracket the experimental value. For both the neutral and anionic ground state species the usual spectroscopic constants were derived.

scholarly journals Dream or Reality: Complete Basis Set Full Configuration Interaction Potential Energy Hypersurfaces

2001 ◽  
pp. 317-339 ◽  
Author(s):  
Attila G. Császár ◽  
György Tarczay ◽  
Matthew L. Leininger ◽  
Oleg L. Polyansky ◽  
Jonathan Tennyson ◽  
...  
Keyword(s):  
Potential Energy ◽  
Interaction Potential ◽  
Configuration Interaction ◽  
Basis Set ◽  
Full Configuration Interaction ◽  
Complete Basis ◽  
Complete Basis Set ◽  
Interaction Potential Energy

Benchmarking Electronic Structure Methods for Accurate Fixed-Charge Electrostatic Models

2019 ◽  
Author(s):  
Alex Zhou ◽  
Michael Schauperl ◽  
Paul Nerenberg
Keyword(s):  
Electronic Structure ◽  
Gas Phase ◽  
Condensed Phase ◽  
Force Fields ◽  
Dipole Moments ◽  
Fixed Charge ◽  
Basis Set ◽  
Atomic Charges ◽  
Molecular Dipole ◽  
Partial Atomic Charges

<p>The accuracy of classical molecular mechanics (MM) force fields used for condensed phase molecular simulations depends strongly on the accuracy of modeling nonbonded interactions between atoms, such as electrostatic interactions. Some popular fixed-charge MM force fields use partial atomic charges derived from gas phase electronic structure calculations using the Hartree-Fock method with the relatively small 6-31G* basis set (HF/6-31G*). It is generally believed that HF/6-31G* generates fortuitously overpolarized electron distributions, as would be expected in the higher dielectric environment of the condensed phase. Using a benchmark set of 47 molecules we show that HF/6-31G* overpolarizes molecules by just under 10% on average with respect to experimental gas phase dipole moments. The overpolarization of this method/basis set combination varies significantly though and, in some cases, even leads to molecular dipole moments that are lower than experimental gas phase measurements. We further demonstrate that using computationally inexpensive density functional theory (DFT) methods, together with appropriate augmented basis sets and a continuum solvent model, can yield molecular dipole moments that are both more strongly and more uniformly overpolarized. These data suggest that these methods – or ones similar to them – should be adopted for the derivation of accurate partial atomic charges for next-generation MM force fields.<br></p>

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