Rodney J. Bartlett

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Name: Bartlett, Rodney J.

Organization: University of Florida , USA

Department: Quantum Theory Project, Departments of Chemistry and Physics

Title: Professor(PhD)

TOPICS

Physical Chemistry

Chemicals
References

Automatic generation of reaction energy databases from highly accurate atomization energy benchmark sets

Co-reporter:Johannes T. Margraf;Duminda S. Ranasinghe

Physical Chemistry Chemical Physics 2017 vol. 19(Issue 15) pp:9798-9805

Publication Date(Web):2017/04/12

DOI:10.1039/C7CP00757D

In this contribution, we discuss how reaction energy benchmark sets can automatically be created from arbitrary atomization energy databases. As an example, over 11 000 reaction energies derived from the W4-11 database, as well as some relevant subsets are reported. Importantly, there is only very modest computational overhead involved in computing >11 000 reaction energies compared to 140 atomization energies, since the rate-determining step for either benchmark is performing the same 140 quantum chemical calculations. The performance of commonly used electronic structure methods for the new database is analyzed. This allows investigating the relationship between the performances for atomization and reaction energy benchmarks based on an identical set of molecules. The atomization energy is found to be a weak predictor for the overall usefulness of a method. The performance of density functional approximations in light of the number of empirically optimized parameters used in their design is also discussed.

Theoretical study of low-lying excited states of HSX (X = F, Cl, Br, I)

Co-reporter:Hengjie Chen, Ajith Perera, Thomas Watson, Rodney J. Bartlett

Chemical Physics Letters 2014 Volume 602() pp:34-39

Publication Date(Web):20 May 2014

DOI:10.1016/j.cplett.2014.04.008

•The excited states of HSX (X = F, Cl, Br, I) are studied, and detailed assignments are investigated.•Benchmarking of parallel EOM-CCSD(T) is performed, also compared with EOM-CCSD, STEOM-CCSD, MS-CASPT2 and MR-CISD.•n → σ∗ or n → Rydberg transitions and single excitations types play a very important role for HSX serials.•The experimental infrared spectra of HSF can be clarified by a straightforward way.The twelve electronic excited states of HSX (X = F, Cl, Br, I) are determined using the equation-of-motion coupled-cluster singles, doubles and with non-iterative triple excitations (EOM-CCSD(T)) method. Comparisons have been made with the two most popular multi-reference methods and detailed assignments are performed. The results show that most excitations of those species originate from the two highest occupied molecular orbitals (n → σ∗ or n → Rydberg transitions), valence like, and predominantly single excitation states. A number of Rydberg states have also been predicted. It is confirmed that the benchmark EOM-CCSD(T) results are in excellent agreement with other theoretical methods.

Gas-Phase Synthesis of Boronylallene (H2CCCH(BO)) under Single Collision Conditions: A Crossed Molecular Beams and Computational Study

Co-reporter:Surajit Maity, Dorian S. N. Parker, and Ralf I. Kaiser, Brad Ganoe, Stefan Fau, Ajith Perera, and Rodney J. Bartlett

The Journal of Physical Chemistry A 2014 Volume 118(Issue 21) pp:3810-3819

Publication Date(Web):May 7, 2014

DOI:10.1021/jp501595n

The gas phase reaction between the boron monoxide radical (11BO; X2Σ+) and allene (H2CCCH2; X1A1) was investigated experimentally under single collision conditions using the crossed molecular beam technique and theoretically exploiting ab initio electronic structure and statistical (RRKM) calculations. The reaction was found to follow indirect (complex forming) scattering dynamics and proceeded via the formation of a van der Waals complex (11BOC3H4). This complex isomerized via addition of the boron monoxide radical (11BO; X2Σ+) with the radical center located at the boron atom to the terminal carbon atom of the allene molecule forming a H2CCCH211BO intermediate on the doublet surface. The chemically activated H2CCCH211BO intermediate underwent unimolecular decomposition via atomic hydrogen elimination from the terminal carbon atom holding the boronyl group through a tight exit transition state to synthesize the boronylallene product (H2CCCH11BO) in a slightly exoergic reaction (55 ± 11 kJ mol–1). Statistical (RRKM) calculations suggest that minor reaction channels lead to the products 3-propynyloxoborane (CH2(11BO)CCH) and 1-propynyloxoborane (CH3CC11BO) with fractions of 1.5% and 0.2%, respectively. The title reaction was also compared with the cyano (CN; X2Σ+)–allene and boronyl–methylacetylene reactions to probe similarities, but also differences of these isoelectronic systems. Our investigation presents a novel gas phase synthesis and characterization of a hitherto elusive organyloxoborane (RBO) monomer—boronylallene—which is inherently tricky to isolate in the condensed phase except in matrix studies; our work further demonstrates that the crossed molecular beams approach presents a useful tool in investigating the chemistry and synthesis of highly reactive organyloxoboranes.

Infinite order relaxation effects for core ionization energies with a variational coupled cluster ansatz

Co-reporter:Thomas J. Watson, Rodney J. Bartlett

Chemical Physics Letters 2013 Volume 555() pp:235-238

Publication Date(Web):3 January 2013

DOI:10.1016/j.cplett.2012.08.046

Abstract

Direct core ionization energies are calculated with a new variational coupled cluster technique. Direct double core ionization energies for orthoaminophenol are also calculated. In this method, the reference function is the ground state N -electron Hartree–Fock determinant, and effects of orbital relaxation are summed to infinite order. This method reproduces the ΔE_SCF $Δ E_{SCF}$ result exactly by changing occupation. An approximation that keeps the occupation constant is demonstrated. The average absolute error for single ionizations using correlation-consistent double and triple-ζ basis sets with this approximation are 0.007 $0.007$ and 0.008 eV, respectively. For double ionizations it is 0.23 eV, under 1% of the relaxation energy.

Benchmarking for Perturbative Triple-Excitations in EE-EOM-CC Methods

Co-reporter:Thomas J. Watson Jr., Victor F. Lotrich, Peter G. Szalay, Ajith Perera, and Rodney J. Bartlett

The Journal of Physical Chemistry A 2013 Volume 117(Issue 12) pp:2569-2579

Publication Date(Web):February 13, 2013

DOI:10.1021/jp308634q

Perturbative triples corrections ((T) and (T̃)) to the equation of motion coupled cluster singles and doubles (EOM-CCSD) are rederived and implemented in a pilot parallel code. The vertical excitation energies of molecules in the test set of Sauer et al. [ J. Chem. Theor. Comput. 2009, 5, 555] are reported and compared to the iterative EOM-CCSDT-3 method. The average absolute deviations of EOM-CCSD(T) and EOM-CCSD(T̃) from EOM-CCSDT-3 over this wide test set are 0.06 and 0.18 eV, respectively. The poor performance of the latter suggests misbalanced handling of the (T̃) terms. Scaling curves for EOM-CCSD(T) are also presented to demonstrate the performance across multiple compute nodes, thus enabling the routine and accurate study of excited states for ever larger molecular systems.

The Great Diversity of HMX Conformers: Probing the Potential Energy Surface Using CCSD(T)

Co-reporter:Robert W. Molt Jr., Thomas Watson Jr., Alexandre P. Bazanté, and Rodney J. Bartlett

The Journal of Physical Chemistry A 2013 Volume 117(Issue 16) pp:3467-3474

Publication Date(Web):March 11, 2013

DOI:10.1021/jp311073m

The octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX) molecule is a very commonly studied system, in all 3 phases, because of its importance as an explosive; however, no one has ever attempted a systematic study of what all the major gas-phase conformers are. This is critical to a mechanistic study of the kinetics involved, as well as the viability of various crystalline polymorphs based on the gas-phase conformers. We have used existing knowledge of basic cyclooctane chemistry to survey all possible HMX conformers based on its fundamental ring structure. After studying what geometries are possible after second-order many-body perturbation theory (MBPT(2)) geometry optimization, we calculated the energetics using coupled cluster singles, doubles, and perturbative triples (CCSD(T))/cc-pVTZ. These highly accurate energies allow us to better calculate starting points for future mechanistic studies. Additionally, the plethora of structures are compared to existing experimental data of crystals. It is found that the crystal field effect is sometimes large and sometimes small for HMX.

Increasing the applicability of DFT I: Non-variational correlation corrections from Hartree–Fock DFT for predicting transition states

Co-reporter:Prakash Verma, Ajith Perera, Rodney J. Bartlett

Chemical Physics Letters 2012 Volume 524() pp:10-15

Publication Date(Web):6 February 2012

DOI:10.1016/j.cplett.2011.12.017

Abstract

Hartree–Fock DFT (HF-DFT) uses the self-interaction error free HF density and DFT functional. Using HF-DFT for molecular structure determination requires a non-variational analytical gradient scheme. This has been developed and applied for the calculation of transition state geometries and barrier heights for chemical reactions. The barrier heights obtained show average absolute errors (AAE) of 2–3 kcal/mol while Λ $Λ$ CCSD(T) show an AAE of 1.1–1.4 kcal/mol. Standard variational DFT with the same functional has AAE’s of 6.3–8.3 kcal/mol while the HF errors are about 12 kcal/mol.

RDX Geometries, Excited States, and Revised Energy Ordering of Conformers via MP2 and CCSD(T) Methodologies: Insights into Decomposition Mechanism

Co-reporter:Robert W. Molt Jr., Thomas Watson Jr., Victor F. Lotrich, and Rodney J. Bartlett

The Journal of Physical Chemistry A 2011 Volume 115(Issue 5) pp:884-890

Publication Date(Web):January 6, 2011

DOI:10.1021/jp109695v

The geometries, harmonic frequencies, elec-tronic excitation levels, and energetic orderings of various conformers of RDX have been computed at the ab initio MP2 and CCSD(T) levels, providing more reliable results than have been previously obtained. We observe that the various local minimum-energy conformers are all competitive for being the absolute minimum and that, at reasonable temperatures, several conformers will appreciably contribute to the population of RDX. As a result, we have concluded that any mechanistic study to investigate thermal decomposition can reasonably begin from any one of the cyclohexane conformers of RDX. As such, it is necessary to consider the transition states for each RDX conformer to gauge what the activation energy is. Homolytic bond dissociation has long been speculated to be critical to detonation; we report here the most accurate estimates of homolytic BDEs yet calculated, likely to be accurate within 3 kcal mol−1. The differences in energy for homolytic BDEs among all the possible RDR conformers are again small, such that most all of the conformers can reasonably be speculated as the next step in the mechanism starting from the RDR radical.

Accuracy of Computed 15N Nuclear Magnetic Resonance Chemical Shifts

Co-reporter:Adriana Gregušová, S. Ajith Perera and Rodney J. Bartlett

Journal of Chemical Theory and Computation 2010 Volume 6(Issue 4) pp:1228-1239

Publication Date(Web):March 4, 2010

DOI:10.1021/ct9005739

Benchmark CCSD(T) 15N NMR calculations are performed for 35 experimentally known 15N shifts of 29 molecules. For the eight known gas phase experimental values of N2, HCN, CH3CN, NNO, NH3, NNO, (CH3)3N, and CH3NH2, CCSD(T) with a basis set previously calibrated for 13C shifts is accurate to 0.2−3 ppm except for the NNO shift, which shows a deviation of 6 ppm. However, the differences between the computed and experimental values in solution due to solvent and finite temperature effects can be as large as ∼25 ppm and must be estimated to relate gas phase 0 K computed values to experiment. An empirical correction is obtained by studying the variations between the estimated solvent effects and the absolute shielding constant. It is shown that the average deviation of computed shifts falls to 3.6 ppm from 12.6 ppm when the correction is applied.

Towards an exact correlated orbital theory for electrons

Co-reporter:Rodney J. Bartlett

Chemical Physics Letters 2009 Volume 484(1–3) pp:1-9

Publication Date(Web):8 December 2009

DOI:10.1016/j.cplett.2009.10.053

Abstract

The formal and computational attraction of effective one-particle theories like Hartree–Fock and density functional theory raise the question of how far such approaches can be taken to offer exact results for selected properties of electrons in atoms, molecules, and solids. Some properties can be exactly described within an effective one-particle theory, like principal ionization potentials and electron affinities. This fact can be used to develop equations for a correlated orbital theory (COT) that guarantees a correct one-particle energy spectrum. They are built upon a coupled-cluster based frequency independent self-energy operator presented here, which distinguishes the approach from Dyson theory. The COT also offers an alternative to Kohn–Sham density functional theory (DFT), whose objective is to represent the electronic density exactly as a single determinant, while paying less attention to the energy spectrum. For any estimate of two-electron terms COT offers a litmus test of its accuracy for principal Ip’s and Ea’s. This feature for approximating the COT equations is illustrated numerically.

First Calculations of 15N−15N J Values and New Calculations of Chemical Shifts for High Nitrogen Systems: A Comment on the Long Search for HN5 and Its Pentazole Anion

Co-reporter:S. Ajith Perera, Adriana Gregušová and Rodney J. Bartlett

The Journal of Physical Chemistry A 2009 Volume 113(Issue 13) pp:3197-3201

Publication Date(Web):March 9, 2009

DOI:10.1021/jp809267y

In the potential solution observation of the long-sought-after pentazole anion (N5−), the principal experimental tool used for detection is NMR. However, in two experiments, very different conclusions were reached. To assist in the interpretation, we report predictive level coupled-cluster results for the spin−spin coupling constants and chemical shifts for all of the key species, which include NO3−, N5−, HN5, N3−, and MeOC6H5N3. In the case of the shifts, an empirical estimate based on the molecule polarity enables comparison of gas-phase and observed values with expected error bars of ∼ ±10 ppm. For the scalar couplings, the evidence is that the solution effects are modest, enabling the gas-phase values (with error bars are ∼ ±5 Hz) to be accurate. The latter supports the observation of centrally 15N labeled N3− in the cerium(IV) ammonium nitrate (CAN) solution which could only occur if the pentazole anion had been created in the experiment, yet with too short a lifetime to be observed in NMR.

Natural Linear-Scaled Coupled-Cluster Theory with Local Transferable Triple Excitations: Applications to Peptides

Co-reporter:Thomas F. Hughes, Norbert Flocke and Rodney J. Bartlett

The Journal of Physical Chemistry A 2008 Volume 112(Issue 26) pp:5994-6003

Publication Date(Web):June 11, 2008

DOI:10.1021/jp800516q

The natural linear-scaled coupled-cluster (NLSCC) method (Flocke, N.Bartlett, R. J. J. Chem. Phys. 2004, 121, 10935) is extended to include approximate triple excitations via a coupled-cluster with single, double, and triple excitation method (CCSDT-3). The triples contribution can potentially be embedded in a larger singles and doubles region. NLSCC exploits the extensivity of the CC wave function to represent it in terms of transferable natural localized molecular orbitals (NLMOs) or functional groups thereof that are obtained from small quantum mechanical (QM) regions. Both occupied and virtual NLMOs are local because they derive from the single-particle density matrix. Noncanonical triples amplitudes are avoided by applying the unitary localization matrix to the canonical CC wave function for a QM region. A generalized NLMO code interfaced to the ACES II quantum chemistry software package provides NLMOs for the relevant number of atoms in a given functional group. Applications include linear polyglycine and the pentapeptide met-enkephalin, which was chosen as a more realistic three-dimensional system with nontrivial side chains. The results show that the triples contributions are quite large for aromatic bonds suggesting an interesting active space method for triples in which different bonds require different excitation levels. The NLSCC approach recovers a very large percentage (>99%) of the CCSD or CCSDT-3 correlation energy.

Intermolecular potential energy surfaces of weakly bound dimers computed from ab initio density functional theory: The right answer for the right reason

Co-reporter:Victor F. Lotrich, Rodney J. Bartlett, Ireneusz Grabowski

Chemical Physics Letters 2005 Volume 405(1–3) pp:43-48

Publication Date(Web):31 March 2005

DOI:10.1016/j.cplett.2005.01.066

Abstract

Ab initio density functional theory has been applied for the weakly interacting, He₂, He–Be²⁺, Ne₂ and Be₂. The results are competitive with the highly accurate coupled-cluster method. The original implementation of the method, which includes correlation, [I. Grabowski, S. Hirata, S. Ivanov, R.J. Bartlett, J. Chem. Phys. 116 (2002) 4415] significantly overestimates the binding in all cases. However, using semi-canonical orbitals as in generalized many-body perturbation theory leads to consistently good potential energy surfaces. The notorious Be dimer potential is about 30% too deep, but virtually parallel to reference results, and much better than MP2.

Co-reporter:S. Ajith Perera

Magnetic Resonance in Chemistry 2001 Volume 39(Issue S1) pp:S183-S189

Publication Date(Web):5 NOV 2001

DOI:10.1002/mrc.911

The equation-of-motion coupled cluster (EOM-CCSD) method was employed to study the variation of proton–proton NMR spin–spin coupling constants with the dihedral angle for coupled protons while all other bond lengths and angles were allowed to relax. N-Methylacetamide was chosen as a frequently studied prototype of substantial experimental interest. The constants (A, B and C) governing the behavior of the coupling constants with the dihedral angle were determined in a fully ab initio, correlated manner and were compared with others in the literature. Copyright © 2001 John Wiley & Sons, Ltd.

Coupled cluster study of the triple bond

Co-reporter:Monika Musiał, Stanisław A. Kucharski, Rodney J. Bartlett

Journal of Molecular Structure: THEOCHEM 2001 Volume 547(1–3) pp:269-278

Publication Date(Web):23 July 2001

DOI:10.1016/S0166-1280(01)00476-6

Several small molecules containing triple bonds have been studied using coupled cluster (CC) methods with inclusion of connected clusters through pentuple excitations. The calculations were performed with a recently developed CC approach that adds noniterative contributions due to the T5 operator to the connected triples and quadruples evaluated in standard CC methods. The results indicate that both for the bond lengths and for the harmonic frequency we observe a slow convergence of the studied property with respect to the cluster expansion. For N2, NO+ and CN− the frequency corrections due to the T4 and T5 clusters at the DZP level are: 20, 5; 19, 7, 10 and 3 cm−1, respectively.

High-order determinantal equation-of-motion coupled-cluster calculations for ionized and electron-attached states

Co-reporter:So Hirata, Marcel Nooijen, Rodney J. Bartlett

Chemical Physics Letters 2000 Volume 328(4–6) pp:459-468

Publication Date(Web):6 October 2000

DOI:10.1016/S0009-2614(00)00965-9

Abstract

General-order equation-of-motion coupled-cluster methods for ionization potentials and electron affinities (IP-EOM-CC and EA-EOM-CC) are developed by employing a determinantal algorithm. With these, principal ionization potentials or electron affinities of diatomic molecules and the excitation energies of their ionized or electron-attached counterparts are computed across different approximations of the cluster operator and the ionization (electron-attachment) operator. IP-EOM-CC(2,2h-1p)=IP-EOM-CCSD and EA-EOM-CC(2,1h-2p)=EA-EOM-CCSD or EA-EOM-CC(2,2h-3p) prove to be well-balanced models for principal ionization potentials and electron affinities, whereas for the quantitative descriptions of non-Koopmans ionization or electron-attachment processes IP-EOM-CC(3,3h-2p)=IP-EOM-CCSDT and EA-EOM-CC(2,2h-3p) appear to be the minimal levels.

The power of exact conditions in electronic structure theory

Co-reporter:Rodney J. Bartlett, Duminda S. Ranasinghe

Chemical Physics Letters (February 2017) Volume 669() pp:

Publication Date(Web):February 2017

DOI:10.1016/j.cplett.2016.12.017

•A ‘consistent’ KS-DFT obtained by insisting IP condition for all occupied orbitals.•IP condition fixes Kohn-Sham potential for each orbital.•IP condition is a consequence of adiabatic TDDFT.•This also means that the ‘multi-electron self-interaction’, is mitigated.Once electron correlation is included in an effective one-particle operator, one has a correlated orbital theory (COT). One such theory is Kohn-Sham density functional theory (KS-DFT), but there are others. Such methods have the prospect to redefine traditional Molecular Orbital (MO) theory by building a quantitative component upon its conceptual framework. This paper asks the question what conditions should such a theory satisfy and can this be accomplished? One such condition for a COT is that the orbital eigenvalues should satisfy an ionization theorem that generalizes Koopmans’ approximation to the exact principal ionization potentials for every electron in a molecule. Guided by this principle, minimal parameterizations of KS-DFT are made that provide a good approximation to a quantitative MO theory.

Automatic generation of reaction energy databases from highly accurate atomization energy benchmark sets

Co-reporter:Johannes T. Margraf, Duminda S. Ranasinghe and Rodney J. Bartlett

Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 15) pp:NaN9805-9805

Publication Date(Web):2017/03/17

DOI:10.1039/C7CP00757D

In this contribution, we discuss how reaction energy benchmark sets can automatically be created from arbitrary atomization energy databases. As an example, over 11000 reaction energies derived from the W4-11 database, as well as some relevant subsets are reported. Importantly, there is only very modest computational overhead involved in computing >11000 reaction energies compared to 140 atomization energies, since the rate-determining step for either benchmark is performing the same 140 quantum chemical calculations. The performance of commonly used electronic structure methods for the new database is analyzed. This allows investigating the relationship between the performances for atomization and reaction energy benchmarks based on an identical set of molecules. The atomization energy is found to be a weak predictor for the overall usefulness of a method. The performance of density functional approximations in light of the number of empirically optimized parameters used in their design is also discussed.