Computational investigation of isomeric and conformeric structures of methyl iodoperoxide

2005 ◽  
Vol 83 (1) ◽  
pp. 9-15 ◽  
Author(s):  
Evangelos Drougas ◽  
Agnie M Kosmas
Keyword(s):  
Electronic Structure ◽  
Single Point ◽  
Transition States ◽  
Vibrational Frequencies ◽  
Basis Sets ◽  
Quantum Mechanical ◽  
Energy Structure ◽  
Computational Investigation ◽  
Electronic Structure Methods ◽  
Optimized Geometries

Quantum mechanical electronic structure methods are employed to investigate the isomeric and conformeric stuctures of methyl iodoperoxide. Optimized geometries and harmonic vibrational frequencies are calculated at the MP2 level of theory using two types of basis sets, the 6-311G(d,p) for all atoms and the 6-311G(d,p) combined with the LANL2DZ relativistic ECP procedure for iodine. Refinement of the energetics has been accomplished by performing single-point CCSD(T) calculations. Five isomers were determined in total among which iodomethyl hydroperoxide (ICH2OOH) is found to be the lowest energy structure. Conformational barriers and transition states that connect the isomeric forms have been characterized.Key words: methyl iodoperoxide, isomers, conformers.

scholarly journals Assessing Conformer Energies using Electronic Structure and Machine Learning Methods

2020 ◽  
Author(s):  
Dakota Folmsbee ◽  
Geoffrey Hutchison
Keyword(s):  
Machine Learning ◽  
Electronic Structure ◽  
Density Functional ◽  
Large Scale ◽  
Single Point ◽  
Semiempirical Method ◽  
Coupled Cluster ◽  
Scale Evaluation ◽  
Machine Learning Methods ◽  
Electronic Structure Methods

We have performed a large-scale evaluation of current computational methods, including conventional small-molecule force fields, semiempirical, density functional, ab initio electronic structure methods, and current machine learning (ML) techniques to evaluate relative single-point energies. Using up to 10 local minima geometries across ~700 molecules, each optimized by B3LYP-D3BJ with single-point DLPNO-CCSD(T) triple-zeta energies, we consider over 6,500 single points to compare the correlation between different methods for both relative energies and ordered rankings of minima. We find promise from current ML methods and recommend methods at each tier of the accuracy-time tradeoff, particularly the recent GFN2 semiempirical method, the B97-3c density functional approximation, and RI-MP2 for accurate conformer energies. The ANI family of ML methods shows promise, particularly the ANI-1ccx variant trained in part on coupled-cluster energies. Multiple methods suggest continued improvements should be expected in both performance and accuracy.

scholarly journals Assessing Conformer Energies using Electronic Structure and Machine Learning Methods

2020 ◽  
Author(s):  
Dakota Folmsbee ◽  
Geoffrey Hutchison
Keyword(s):  
Machine Learning ◽  
Electronic Structure ◽  
Density Functional ◽  
Large Scale ◽  
Single Point ◽  
Semiempirical Method ◽  
Coupled Cluster ◽  
Scale Evaluation ◽  
Machine Learning Methods ◽  
Electronic Structure Methods

We have performed a large-scale evaluation of current computational methods, including conventional small-molecule force fields, semiempirical, density functional, ab initio electronic structure methods, and current machine learning (ML) techniques to evaluate relative single-point energies. Using up to 10 local minima geometries across ~700 molecules, each optimized by B3LYP-D3BJ with single-point DLPNO-CCSD(T) triple-zeta energies, we consider over 6,500 single points to compare the correlation between different methods for both relative energies and ordered rankings of minima. We find promise from current ML methods and recommend methods at each tier of the accuracy-time tradeoff, particularly the recent GFN2 semiempirical method, the B97-3c density functional approximation, and RI-MP2 for accurate conformer energies. The ANI family of ML methods shows promise, particularly the ANI-1ccx variant trained in part on coupled-cluster energies. Multiple methods suggest continued improvements should be expected in both performance and accuracy.

Ab initio molecular orbital study of simple 1,3-dipolar reactions

1976 ◽  
Vol 29 (3) ◽  
pp. 465 ◽  
Author(s):  
D Poppinger
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Transition States ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Molecular Orbital Study ◽  
Orbital Study ◽  
Extended Basis ◽  
Optimized Geometries

Ab initio molecular orbital calculations with minimal and extended basis sets have been carried out for the 1,3-dipolar addition of fulminic acid to acetylene, ethylene, ethynamine and propynenitrile. Optimized geometries are reported for the transition states HCNO+C2H2, HCNO+C2H4, HCNO+ C2HNH2, for the adducts isoxazole and 2-isoxazoline, and for nitrosocyclopropene as a possible intermediate. The calculations indicate that (a) these 1,3-dipolar reactions are synchronous processes, (b) the geometry of the transition state is insensitive to substitution and (c) of the isomeric substituted adducts, 5-aminoisoxazole and isoxazole-4-carbonitrile should be formed preferentially.

scholarly journals The Performance of Dunning, Jensen and Karlsruhe Basis Sets on Computing Relative Energies and Geometries

2019 ◽  
Author(s):  
Karl Kirschner ◽  
Dirk Reith ◽  
Wolfgang Heiden
Keyword(s):  
Systematic Study ◽  
Transition States ◽  
Water Dimer ◽  
Basis Set ◽  
Basis Sets ◽  
Quantum Mechanical ◽  
Mechanical Modeling ◽  
Molecular Systems ◽  
Speed And Accuracy ◽  
Do So

<div>In an effort to assist researchers in choosing basis sets for quantum mechanical modeling of molecules (i.e. balancing calculation cost versus desired accuracy), we present a systematic study on the accuracy of computed conformational relative energies and their geometries in comparison to MP2/CBS and MP2/AV5Z data, respectively. In order to do so, we introduce a new nomenclature to unambiguously indicate how a CBS extrapolation was computed. Nineteen minima and transition states of buta-1,3-diene, propan-2-ol and the water dimer were optimized using forty-five different basis sets. Specifically, this includes one Pople (i.e. 6-31G(d)), eight Dunning (i.e. VXZ and AVXZ, X=2-5), twenty-five Jensen (i.e. pc-n, pcseg-n, aug-pcseg-n, pcSseg-n and aug-pcSseg-n, n=0-4) and nine Karlsruhe (e.g. def2-SV(P), def2-QZVPPD) basis sets. The molecules were chosen to represent both common and electronically diverse molecular systems. In comparison to MP2/CBS relative energies computed using the largest Jensen basis sets (i.e. n=2,3,4), the use of smaller sizes (n=0,1,2 and n=1,2,3) provides results that are within 0.11--0.24 and 0.09-0.16 kcal/mol. To practically guide researchers in their basis set choice, an equation is introduced that ranks basis sets based on a user-defined balance between their accuracy and calculation cost. Furthermore, we explain why the aug-pcseg-2, def2-TZVPPD and def2-TZVP basis sets are very suitable choices to balance speed and accuracy.</div>

scholarly journals The Performance of Dunning, Jensen and Karlsruhe Basis Sets on Computing Relative Energies and Geometries

2019 ◽  
Author(s):  
Karl Kirschner ◽  
Dirk Reith ◽  
Wolfgang Heiden
Keyword(s):  
Systematic Study ◽  
Transition States ◽  
Water Dimer ◽  
Basis Set ◽  
Basis Sets ◽  
Quantum Mechanical ◽  
Mechanical Modeling ◽  
Molecular Systems ◽  
Speed And Accuracy ◽  
Do So

<div>In an effort to assist researchers in choosing basis sets for quantum mechanical modeling of molecules (i.e. balancing calculation cost versus desired accuracy), we present a systematic study on the accuracy of computed conformational relative energies and their geometries in comparison to MP2/CBS and MP2/AV5Z data, respectively. In order to do so, we introduce a new nomenclature to unambiguously indicate how a CBS extrapolation was computed. Nineteen minima and transition states of buta-1,3-diene, propan-2-ol and the water dimer were optimized using forty-five different basis sets. Specifically, this includes one Pople (i.e. 6-31G(d)), eight Dunning (i.e. VXZ and AVXZ, X=2-5), twenty-five Jensen (i.e. pc-n, pcseg-n, aug-pcseg-n, pcSseg-n and aug-pcSseg-n, n=0-4) and nine Karlsruhe (e.g. def2-SV(P), def2-QZVPPD) basis sets. The molecules were chosen to represent both common and electronically diverse molecular systems. In comparison to MP2/CBS relative energies computed using the largest Jensen basis sets (i.e. n=2,3,4), the use of smaller sizes (n=0,1,2 and n=1,2,3) provides results that are within 0.11--0.24 and 0.09-0.16 kcal/mol. To practically guide researchers in their basis set choice, an equation is introduced that ranks basis sets based on a user-defined balance between their accuracy and calculation cost. Furthermore, we explain why the aug-pcseg-2, def2-TZVPPD and def2-TZVP basis sets are very suitable choices to balance speed and accuracy.</div>

scholarly journals The Performance of Dunning, Jensen and Karlsruhe Basis Sets on Computing Relative Energies and Geometries

2019 ◽  
Author(s):  
Karl Kirschner ◽  
Dirk Reith ◽  
Wolfgang Heiden
Keyword(s):  
Systematic Study ◽  
Transition States ◽  
Water Dimer ◽  
Basis Set ◽  
Basis Sets ◽  
Quantum Mechanical ◽  
Mechanical Modeling ◽  
Molecular Systems ◽  
Speed And Accuracy ◽  
Do So

<div>In an effort to assist researchers in choosing basis sets for quantum mechanical modeling of molecules (i.e. balancing calculation cost versus desired accuracy), we present a systematic study on the accuracy of computed conformational relative energies and their geometries in comparison to MP2/CBS and MP2/AV5Z data, respectively. In order to do so, we introduce a new nomenclature to unambiguously indicate how a CBS extrapolation was computed. Nineteen minima and transition states of buta-1,3-diene, propan-2-ol and the water dimer were optimized using forty-five different basis sets. Specifically, this includes one Pople (i.e. 6-31G(d)), eight Dunning (i.e. VXZ and AVXZ, X=2-5), twenty-five Jensen (i.e. pc-n, pcseg-n, aug-pcseg-n, pcSseg-n and aug-pcSseg-n, n=0-4) and nine Karlsruhe (e.g. def2-SV(P), def2-QZVPPD) basis sets. The molecules were chosen to represent both common and electronically diverse molecular systems. In comparison to MP2/CBS relative energies computed using the largest Jensen basis sets (i.e. n=2,3,4), the use of smaller sizes (n=0,1,2 and n=1,2,3) provides results that are within 0.11--0.24 and 0.09-0.16 kcal/mol. To practically guide researchers in their basis set choice, an equation is introduced that ranks basis sets based on a user-defined balance between their accuracy and calculation cost. Furthermore, we explain why the aug-pcseg-2, def2-TZVPPD and def2-TZVP basis sets are very suitable choices to balance speed and accuracy.</div>

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