Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2020
As noted in Wikipedia,skin in the gamerefers to having ‘incurred risk by being involved in achiev... more As noted in Wikipedia,skin in the gamerefers to having ‘incurred risk by being involved in achieving a goal’, where ‘skinis a synecdoche for the person involved, andgameis the metaphor for actions on the field of play under discussion’. For exascale applications under development in the US Department of Energy Exascale Computing Project, nothing could be more apt, with theskinbeing exascale applications and thegamebeing delivering comprehensive science-based computational applications that effectively exploit exascale high-performance computing technologies to provide breakthrough modelling and simulation and data science solutions. These solutions will yield high-confidence insights and answers to the most critical problems and challenges for the USA in scientific discovery, national security, energy assurance, economic competitiveness and advanced healthcare.This article is part of a discussion meeting issue ‘Numerical algorithms for high-performance computational science’.
The tight d-augmented correlation consistent basis sets, cc-pV (n+ d) Z, and standard correlation... more The tight d-augmented correlation consistent basis sets, cc-pV (n+ d) Z, and standard correlation consistent basis sets, cc-pV n Z, where n= D (2), T (3), Q (4), and 5, for the second-row atoms have been used to re-examine the relative energy of the HSO and SOH ...
The electron affinity of NO has been measured to be 0.026 eV by laser photodetachment experiments... more The electron affinity of NO has been measured to be 0.026 eV by laser photodetachment experiments. This low electron affinity (just 2.5 kJ/mol or 210 cm-1) presents a computational challenge that requires careful attention to several aspects of the computational procedure required to predict the electron affinity of NO from first principles. We have used augmented correlation consistent basis sets with several coupled cluster methods to calculate the molecular energies, bond dissociation energies, bond lengths, vibrational frequencies, and potential energy curves for NO and NO-. The electron affinity of NO, EA0, using the CCSD(T) method and extrapolating to the complete basis set limit, is calculated to be 0.028 eV. The calculated bond dissociation energies, D0, for NO and NO- are 622 and 487 kJ/mol, respectively, compared with experimental values of 626.8 and 487.8 kJ/mol. From the calculated potential energy curves for NO and NO- the vibrational wavefunctions were determined. The calculated vibrational wavefunctions predict Franck-Condon factor ratios in good agreement with the values determined in the photodetachment experiment.
Potential energy surfaces have been determined for the A′ and A″ states of the He(1S)+CH(X 2Π) sy... more Potential energy surfaces have been determined for the A′ and A″ states of the He(1S)+CH(X 2Π) system. The interaction energies were computed using a Hartree–Fock singles and doubles CI treatment; convergence of the calculation with respect to both basis set and configuration set was investigated. The surfaces have been represented quantitatively by standard Legendre polynomial expansions and qualitatively by novel pairwise additive potentials. With the pairwise additive models, successful fits require that the centers of force be orbital based as opposed to the typical nucleus-based form. Comparison of the surfaces would suggest that the final fitted surfaces are accurate to a few tenths of a kcal/mol up to 5–10 kcal/mol. In the following paper, the dynamical consequences of the small differences between all the surfaces will be assessed by quantum dynamics calculations of cross sections and their subsequent comparison to experiment.
An explicit treatment of electron correlation is required to predict accurate energetics, barrier... more An explicit treatment of electron correlation is required to predict accurate energetics, barrier heights, and saddle point geometries for chemical reactions. Several theoretical methods for treating electron correlation (multireference configuration interaction, perturbation theory, and coupled cluster methods) have been thoroughly evaluated for the F(2P) + H2(X1Σg+) and O(3P) + H2(X1Σg+) abstraction reactions as well as for the H‘(2S) + HCl(X1Σ+) exchange reaction using correlation consistent basis sets. The basis set dependence of the reaction energy defects, barrier heights, and saddle point geometries have been determined for each theoretical method. Addition of diffuse functions to the basis set (aug-cc-pVnZ) was found to substantially increase the convergence rate. Calculations with the largest basis set (aug-cc-pV5Z) allowed an unambiguous comparison of the relative performance of each correlation method. For each reaction, the R-UCCSD(T) results closely parallel the most accurate MRCI results and...
Author Institution: Department of Chemistry, California Institute of TechnologyThe effects of spa... more Author Institution: Department of Chemistry, California Institute of TechnologyThe effects of spatial symmetry restrictions upon the calculated values of the hyperfine splitting constants is examined and numerical results are presented for the B, C, O, and F atoms. If no symmetry restrictions are placed upon the unrestricted Hartree-Fock orbitals, the resulting hyperfine constants (except spin densities) are in good agreement with experiment and with extensive configuration calculations. This relaxation of symmetry conditions should also be important for obtaining accurate hyperfine constants for linear molecules
Using systematic sequences of correlation consistent basis sets, the accuracy of calculated bond ... more Using systematic sequences of correlation consistent basis sets, the accuracy of calculated bond energies De(CH) and equilibrium geometries (re, θe) has been investigated for the CHn and C2Hn series (n=1–4). Perturbation theory (MP2, MP3, MP4), coupled cluster [CCSD, CCSD(T)], and single and multireference configuration interaction (HF+1+2, CAS+1+2) methods have been investigated. Except for the vinyl radical, all of the calculated bond energies showed significant basis set dependence with average errors (standard deviations) of 5.6 (±3.0) kcal/mol for the cc-pVDZ set, 1.4 (±0.8) kcal/mol for the cc-pVTZ set, and 0.5 (±0.4) kcal/mol for the cc-pVQZ set with CCSD(T) wave functions. For the vinyl radical the total variation with basis set was just 0.6 kcal/mol. Strong basis set dependence was also observed for the equilibrium geometries, e.g., for re(CH) the average error decreased from 0.020 Å (cc-pVDZ) to 0.003 Å (cc-pVTZ) to 0.002 Å (cc-pVQZ). The effect of including the core electrons in the correlated calculations was also investigated for the two series. Inclusion of core correlation in the CHn series increased De(CH) by 0.13 (CH) to 0.61 kcal/mol (CH2) and decreased the equilibrium CH bond lengths by approximately 0.0015 Å. For the C2Hn series, correlation of the core electrons increased De(CH) by 0.18 (C2H4) to 1.01 (C2H) kcal/mol, but decreased De(CH) in C2H2 by 0.25 kcal/mol. Predictions are also made for the equilibrium geometries of C2H, H2CC, and C2H3, as well as the CH bond strength of vinylidene and the acetylene–vinylidene isomerization energy.
Potential energy functions have been calculated for the electronic ground states of the first row... more Potential energy functions have been calculated for the electronic ground states of the first row diatomic hydrides BH, CH, NH, OH, and HF using single- (HF+1+2) and multi- (GVB+1+2 and CAS+1+2) reference internally contracted single and double excitation configuration interaction (CI) wave functions. The convergence of the derived spectroscopic constants and dissociation energies with respect to systematic increases in the size of the one-particle basis set has been investigated for each method using the correlation consistent basis sets of Dunning and co-workers. The effect of augmenting the basis sets with extra diffuse functions has also been addressed. Using sets of double (cc-pVDZ) through quintuple (cc-pV5Z) zeta quality, the complete basis set (CBS) limits for Ee, De, re, and ωe have been estimated for each theoretical method by taking advantage of the regular convergence behavior. The estimated CBS limits are compared to the available experimental results, and the intrinsic errors associated with each theoretical method are discussed. The potential energy functions obtained from GVB+1+2 and CAS+1+2 calculations are observed to yield very comparable spectroscopic constants, with errors in De ranging from 0.4 kcal/mol for BH to 2.9 kcal/mol for HF. The contraction errors associated with the internally contracted multireference CI have also been calculated for each species; while found to increase from BH to HF, they are, in general, small for all calculated spectroscopic constants. For the cc-pVDZ basis sets, spectroscopic constants have also been determined from full CI calculations.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2020
As noted in Wikipedia,skin in the gamerefers to having ‘incurred risk by being involved in achiev... more As noted in Wikipedia,skin in the gamerefers to having ‘incurred risk by being involved in achieving a goal’, where ‘skinis a synecdoche for the person involved, andgameis the metaphor for actions on the field of play under discussion’. For exascale applications under development in the US Department of Energy Exascale Computing Project, nothing could be more apt, with theskinbeing exascale applications and thegamebeing delivering comprehensive science-based computational applications that effectively exploit exascale high-performance computing technologies to provide breakthrough modelling and simulation and data science solutions. These solutions will yield high-confidence insights and answers to the most critical problems and challenges for the USA in scientific discovery, national security, energy assurance, economic competitiveness and advanced healthcare.This article is part of a discussion meeting issue ‘Numerical algorithms for high-performance computational science’.
The tight d-augmented correlation consistent basis sets, cc-pV (n+ d) Z, and standard correlation... more The tight d-augmented correlation consistent basis sets, cc-pV (n+ d) Z, and standard correlation consistent basis sets, cc-pV n Z, where n= D (2), T (3), Q (4), and 5, for the second-row atoms have been used to re-examine the relative energy of the HSO and SOH ...
The electron affinity of NO has been measured to be 0.026 eV by laser photodetachment experiments... more The electron affinity of NO has been measured to be 0.026 eV by laser photodetachment experiments. This low electron affinity (just 2.5 kJ/mol or 210 cm-1) presents a computational challenge that requires careful attention to several aspects of the computational procedure required to predict the electron affinity of NO from first principles. We have used augmented correlation consistent basis sets with several coupled cluster methods to calculate the molecular energies, bond dissociation energies, bond lengths, vibrational frequencies, and potential energy curves for NO and NO-. The electron affinity of NO, EA0, using the CCSD(T) method and extrapolating to the complete basis set limit, is calculated to be 0.028 eV. The calculated bond dissociation energies, D0, for NO and NO- are 622 and 487 kJ/mol, respectively, compared with experimental values of 626.8 and 487.8 kJ/mol. From the calculated potential energy curves for NO and NO- the vibrational wavefunctions were determined. The calculated vibrational wavefunctions predict Franck-Condon factor ratios in good agreement with the values determined in the photodetachment experiment.
Potential energy surfaces have been determined for the A′ and A″ states of the He(1S)+CH(X 2Π) sy... more Potential energy surfaces have been determined for the A′ and A″ states of the He(1S)+CH(X 2Π) system. The interaction energies were computed using a Hartree–Fock singles and doubles CI treatment; convergence of the calculation with respect to both basis set and configuration set was investigated. The surfaces have been represented quantitatively by standard Legendre polynomial expansions and qualitatively by novel pairwise additive potentials. With the pairwise additive models, successful fits require that the centers of force be orbital based as opposed to the typical nucleus-based form. Comparison of the surfaces would suggest that the final fitted surfaces are accurate to a few tenths of a kcal/mol up to 5–10 kcal/mol. In the following paper, the dynamical consequences of the small differences between all the surfaces will be assessed by quantum dynamics calculations of cross sections and their subsequent comparison to experiment.
An explicit treatment of electron correlation is required to predict accurate energetics, barrier... more An explicit treatment of electron correlation is required to predict accurate energetics, barrier heights, and saddle point geometries for chemical reactions. Several theoretical methods for treating electron correlation (multireference configuration interaction, perturbation theory, and coupled cluster methods) have been thoroughly evaluated for the F(2P) + H2(X1Σg+) and O(3P) + H2(X1Σg+) abstraction reactions as well as for the H‘(2S) + HCl(X1Σ+) exchange reaction using correlation consistent basis sets. The basis set dependence of the reaction energy defects, barrier heights, and saddle point geometries have been determined for each theoretical method. Addition of diffuse functions to the basis set (aug-cc-pVnZ) was found to substantially increase the convergence rate. Calculations with the largest basis set (aug-cc-pV5Z) allowed an unambiguous comparison of the relative performance of each correlation method. For each reaction, the R-UCCSD(T) results closely parallel the most accurate MRCI results and...
Author Institution: Department of Chemistry, California Institute of TechnologyThe effects of spa... more Author Institution: Department of Chemistry, California Institute of TechnologyThe effects of spatial symmetry restrictions upon the calculated values of the hyperfine splitting constants is examined and numerical results are presented for the B, C, O, and F atoms. If no symmetry restrictions are placed upon the unrestricted Hartree-Fock orbitals, the resulting hyperfine constants (except spin densities) are in good agreement with experiment and with extensive configuration calculations. This relaxation of symmetry conditions should also be important for obtaining accurate hyperfine constants for linear molecules
Using systematic sequences of correlation consistent basis sets, the accuracy of calculated bond ... more Using systematic sequences of correlation consistent basis sets, the accuracy of calculated bond energies De(CH) and equilibrium geometries (re, θe) has been investigated for the CHn and C2Hn series (n=1–4). Perturbation theory (MP2, MP3, MP4), coupled cluster [CCSD, CCSD(T)], and single and multireference configuration interaction (HF+1+2, CAS+1+2) methods have been investigated. Except for the vinyl radical, all of the calculated bond energies showed significant basis set dependence with average errors (standard deviations) of 5.6 (±3.0) kcal/mol for the cc-pVDZ set, 1.4 (±0.8) kcal/mol for the cc-pVTZ set, and 0.5 (±0.4) kcal/mol for the cc-pVQZ set with CCSD(T) wave functions. For the vinyl radical the total variation with basis set was just 0.6 kcal/mol. Strong basis set dependence was also observed for the equilibrium geometries, e.g., for re(CH) the average error decreased from 0.020 Å (cc-pVDZ) to 0.003 Å (cc-pVTZ) to 0.002 Å (cc-pVQZ). The effect of including the core electrons in the correlated calculations was also investigated for the two series. Inclusion of core correlation in the CHn series increased De(CH) by 0.13 (CH) to 0.61 kcal/mol (CH2) and decreased the equilibrium CH bond lengths by approximately 0.0015 Å. For the C2Hn series, correlation of the core electrons increased De(CH) by 0.18 (C2H4) to 1.01 (C2H) kcal/mol, but decreased De(CH) in C2H2 by 0.25 kcal/mol. Predictions are also made for the equilibrium geometries of C2H, H2CC, and C2H3, as well as the CH bond strength of vinylidene and the acetylene–vinylidene isomerization energy.
Potential energy functions have been calculated for the electronic ground states of the first row... more Potential energy functions have been calculated for the electronic ground states of the first row diatomic hydrides BH, CH, NH, OH, and HF using single- (HF+1+2) and multi- (GVB+1+2 and CAS+1+2) reference internally contracted single and double excitation configuration interaction (CI) wave functions. The convergence of the derived spectroscopic constants and dissociation energies with respect to systematic increases in the size of the one-particle basis set has been investigated for each method using the correlation consistent basis sets of Dunning and co-workers. The effect of augmenting the basis sets with extra diffuse functions has also been addressed. Using sets of double (cc-pVDZ) through quintuple (cc-pV5Z) zeta quality, the complete basis set (CBS) limits for Ee, De, re, and ωe have been estimated for each theoretical method by taking advantage of the regular convergence behavior. The estimated CBS limits are compared to the available experimental results, and the intrinsic errors associated with each theoretical method are discussed. The potential energy functions obtained from GVB+1+2 and CAS+1+2 calculations are observed to yield very comparable spectroscopic constants, with errors in De ranging from 0.4 kcal/mol for BH to 2.9 kcal/mol for HF. The contraction errors associated with the internally contracted multireference CI have also been calculated for each species; while found to increase from BH to HF, they are, in general, small for all calculated spectroscopic constants. For the cc-pVDZ basis sets, spectroscopic constants have also been determined from full CI calculations.
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