Gaussian Basis Sets for Highly Accurate Calculations of Isotropic Hyperfine Coupling Constants at Hydrogen

Fau, Stefan; Bartlett, Rodney J.

doi:10.1021/jp0276294

Cited by 23 publications

(30 citation statements)

References 34 publications

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“…This, as well as the relatively large difference between UHF-and ROHF-based CCSD values, suggests that the core/inner-valence region of the carbon basis sets is not flexible enough. 6,46 The hydrogen iHFCCs of H 2 CN • (Figure 3; Supporting Information, Table S9) change by 0.2 G or less in the presence of core-correlation functions. Using an ROHF reference changes them by just 0.2 G at the CCSD level but by 1.0 to 1.3 G at CCSD(T).…”

Section: Isotropic Hyperfine Coupling Constants At the Uccsdt/ Cbs3 Gmentioning

confidence: 99%

“…More details about the calculation of spin densities and reasons for the basis set requirements for calculating iHFCCs are given in the preceding article. 6 Several research groups have attempted the calculation of quantitatively accurate HFC constants of organic radicals using a variety of methods and basis sets. Chipman 2 developed a method that is closely related to ROHF-CIS and considers mainly spin polarization effects.…”

Section: Introductionmentioning

confidence: 99%

“…Depending on the degree of contraction, the t5s basis sets' performance is good to excellent for H • , H 2 +• , and H 4 +• . 6 The t5s-a(v+3) basis sets (v is the number of s functions in the parent basis set: 2 for cc-pVDZ, 3 for aug-cc-pVDZ and cc-pVTZ, ...) perform as excellently as the uncontracted basis sets, and the t5s-a(v+2) basis sets are very nearly as good. More contracted basis sets such as cc-pVDZ-t5s-c3 and -c2 show larger errors but still remedy the systematic underestimation of isotropic HFCCs exhibited by the parent basis sets.…”

Section: Introductionmentioning

confidence: 99%

“…More contracted basis sets such as cc-pVDZ-t5s-c3 and -c2 show larger errors but still remedy the systematic underestimation of isotropic HFCCs exhibited by the parent basis sets. 6 Although the correlation method, basis set, and geometry are recognized as being important factors (see references cited in ref [1][2][3][4], they tend to be investigated separately. We do not know of any systematic study that investigates the dependence of the iHFCCs of organic radicals upon geometry, basis set, and correlation.…”

Section: Introductionmentioning

confidence: 99%

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Benchmark Study of Isotropic Hyperfine Coupling Constants for Hydrogen: Influence of Geometry, Correlation Method, and Basis Set

2003

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Isotropic hyperfine coupling constants (iHFCCs) can be easily measured by electron spin resonance spectroscopy in solution, but they have proven difficult to calculate from first principles. We test the performance of the newly developed (aug-)cc-pVXZ-t5s basis sets for hydrogen with Dunning's (aug-)cc-pVXZ and -pCVXZ basis sets for non-hydrogen atoms. Correlation is included by CCSD and CCSD(T) using UHF and ROHF references. A two-point extrapolation of cc-pVDZ:cc-pVDZ-t5s-a5 and cc-pVTZ:cc-pVTZ-t5s-a6 hydrogen iHFCCs is found to be very useful. Diffuse functions have nearly no influence on extrapolated iHFCCs. We also explore the dependence of the calculated iHFCCs on the level of theory used in optimizing the geometries. For this purpose, we optimized geometries up to the UHF-CCSD/cc-pCVQZ and UHF-CCSDT/cc-pCVTZ levels and extrapolated to the "complete basis set" limit. The calculated iHFCCs are compared to reference values, which are experimental numbers corrected for solvent and the most important vibrational effects. Our test molecules are the CH 3 • , C 2 H 3 • , and H 2 CN • radicals. At the highest level of theory, the largest deviations from the reference values are smaller than 3.5 G and 6%. The rms errors are below 2.1 G and 4%. The cc-pVXZ:cc-pVXZ-t5s basis set combinations perform better than the EPR-n and the Chipman [631|41] basis set. All of them are better than similarly sized basis sets that were not developed for iHFCCs. The calculated iHFCCs are influenced most strongly by the choice of basis set, the perturbative inclusion of connected triple excitations, and the choice of reference wave function and the level of theory in geometry optimization. Core correlation is necessary for the computation of iHFCCs for non-hydrogen atoms but has very little influence on the iHFCCs of hydrogen atoms. A good compromise between the cost and accuracy of hydrogen iHFCCs seems to be reached by two-point extrapolated ROHF-CCSD(T)-fc iHFCCs at UHF-MBPT(2)-fc/cc-pVTZ geometries. ROHF-MBPT(2)-fc or UHF-CCSD-fc/cc-pVTZ geometries are necessary when single excitations are not negligible.

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Section: Isotropic Hyperfine Coupling Constants At the Uccsdt/ Cbs3 Gmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Benchmark Study of Isotropic Hyperfine Coupling Constants for Hydrogen: Influence of Geometry, Correlation Method, and Basis Set

2003

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“…All electrons were correlated in the geometry optimizations. Following previous suggestions, 33,34 we have used in our calculations of spin densities the aug-cc-pCVXZ (augcc-pVXZ for hydrogen) basis set 35 (X = T,Q) with uncontracted s functions and added a set of five even-tempered s functions that are obtained by multiplying the coefficient of the tightest s primitive in the aug-cc-pCVXZ basis set by 5 n (n = 1 − 5). These basis sets are denoted in the following as aCVXZ-su5 (aVXZ-su5 for H) in analogy with Refs.…”

mentioning

confidence: 99%