About

Rodney J. Bartlett is a Graduate Research Professor in the Department of Chemistry at the University of Florida. His research has pioneered coupled-cluster (CC) theory and its equation-of-motion extensions, enabling highly accurate predictions of molecular structures and spectra. His group developed the widely used ACES II and III program systems and applied CC theory to predict and identify novel high-energy molecules such as N5–, N5O+, and N8. Bartlett provided the first predictive-quality theoretical values for non-linear optics and NMR couplings, resolving discrepancies between theory and experiment. His team also developed natural linear scaled CC, correlated quantum chemical methods for polymers, the transfer Hamiltonian for materials, and correlated orbital theory (COT), which defines the QTP family of density functionals. His extensive contributions have significantly advanced the field of theoretical and computational chemistry.

Research topics

• Computer Science
• Statistical physics
• Physics
• Quantum mechanics
• Programming language
• Parallel computing
• Mathematics
• Statistics
• Software engineering
• Atomic physics
• Geometry

Selected publications

• On the performance of QTP functionals applied to second-order response properties II: Dynamic polarizability and long-range C$_6$ coefficients

  ArXiv.org · 2026-03-16

  articleOpen accessSenior author

  This work is the second in the series "On the performance of QTP functionals applied to second-order response properties." In the first paper (J. Chem. Phys. 162, 054105, 2025), we demonstrated the good performance of Quantum Theory Project functionals in predicting static perturbed second-order properties, such as static polarizabilities, nuclear magnetic resonance (NMR) spin-spin coupling constants, and NMR chemical shifts. In the present study, we focus on frequency-dependent properties, namely dynamic polarizabilities and C$_6$ dispersion coefficients. For completeness, a total of 25 exchange-correlation (XC) functionals were investigated. Dynamic polarizabilities were evaluated at five different perturbation wavelengths: 632.99 nm, 594.10 nm, 543.52 nm, 514.50 nm, and 325.13 nm. This property was also computed using HF and EOM-CCSD. In general, EOM-CCSD results are very close to those obtained with linear-response CC3, except at the highest frequency. Among Kohn-Sham calculations, TPSS0 and QTP01 showed the best overall performance for dynamic polarizabilities. We also assessed how well QTP functionals reproduce the pole structure of the CO molecule. For the C$_6$ dispersion coefficients, calculations were performed using the Casimir-Polder equation. The best overall performance was obtained with O3LYP; however, the first eleven ranked functionals show very similar accuracy. Within the QTP family, QTP01 and LC-QTP provide the best results for C$_6$ coefficients.

  PublisherOA PDF

• On the performance of QTP functionals applied to second-order response properties II: Dynamic polarizability and long-range C$_6$ coefficients

  arXiv (Cornell University) · 2026-03-16

  preprintOpen accessSenior author

  This work is the second in the series "On the performance of QTP functionals applied to second-order response properties." In the first paper (J. Chem. Phys. 162, 054105, 2025), we demonstrated the good performance of Quantum Theory Project functionals in predicting static perturbed second-order properties, such as static polarizabilities, nuclear magnetic resonance (NMR) spin-spin coupling constants, and NMR chemical shifts. In the present study, we focus on frequency-dependent properties, namely dynamic polarizabilities and C$_6$ dispersion coefficients. For completeness, a total of 25 exchange-correlation (XC) functionals were investigated. Dynamic polarizabilities were evaluated at five different perturbation wavelengths: 632.99 nm, 594.10 nm, 543.52 nm, 514.50 nm, and 325.13 nm. This property was also computed using HF and EOM-CCSD. In general, EOM-CCSD results are very close to those obtained with linear-response CC3, except at the highest frequency. Among Kohn-Sham calculations, TPSS0 and QTP01 showed the best overall performance for dynamic polarizabilities. We also assessed how well QTP functionals reproduce the pole structure of the CO molecule. For the C$_6$ dispersion coefficients, calculations were performed using the Casimir-Polder equation. The best overall performance was obtained with O3LYP; however, the first eleven ranked functionals show very similar accuracy. Within the QTP family, QTP01 and LC-QTP provide the best results for C$_6$ coefficients.

  PublisherDOI

• Does correlated orbital theory improve PBE-like functionals?

  The Journal of Chemical Physics · 2026-02-06

  articleSenior author

  Correlated Orbital Theory (COT) provides an exact one-particle framework by imposing rigorous physical constraints on Kohn-Sham eigenvalues and, as a consequence, directly incorporates essential electron correlation into molecular orbitals. This approach paves the way toward a new class of approximations within Kohn-Sham Density Functional Theory (KS-DFT). However, since all existing quantum theory project functionals are derived from CAM-B3LYP, we pose the question: Can COT improve the hybrid versions of different exchange-correlation functionals as well? To that end, we explore two optimization strategies for adjusting the existing parameters within PBE0, TPSS0, and LC-PBE0: (i) the ionization potential condition and (ii) the HOMO-LUMO condition. In this sense, we critically assess how these functionals address the "Devil's Triangle" of KS-DFT: self-interaction error, integer discontinuity, and one-particle spectra. We further examine how the COT influences the description of two challenging properties, charge transfer and reaction barrier heights. Overall, enforcing both COT conditions systematically enhances the performance of functionals within the PBE family, although the description of reaction barriers still leaves room for improvement.

  PublisherDOI

• Toward the “platinum standard” of quantum chemistry on quantum computers: Perturbative quadruple corrections in unitary coupled cluster theory

  The Journal of Chemical Physics · 2026-01-02 · 1 citations

  articleSenior author

  We propose a non-iterative, post-hoc correction to the unitary coupled cluster theory with the single, double, and triple excitations (UCCSDT) Ansatz, which considers the leading-order effects of neglected quadruple excitations. We present two ways to derive this correction, henceforth referred to as [Q-6], which leads to an improvement in the correlation energy shown to be truncated to sixth-order in many-body perturbation theory. A comparison between the UCC-based [Q-6] correction proposed in this work and analogous, "platinum standard" quadruple corrections proposed in conventional coupled cluster theory recognizes that [Q-6] is distinct from prior corrections since it is constructed entirely from internally connected components. Although trotterized (t) and full operator variants of UCCSDT exhibit errors in scans of small molecule potential energy surfaces that routinely exceed 1.6 mH, we find that t/UCCSDT[Q-6] is, nevertheless, able to achieve chemical accuracy as measured by the mean unsigned error.

  PublisherDOI

• On the Performance of QTP Functionals Applied to Second-Order Response Properties II: Dynamic Polarizability and Long-Range C ₆ Coefficients

  The Journal of Physical Chemistry A · 2026-05-20

  articleSenior author

  coefficients.

  PublisherDOI

• Does Correlated Orbital Theory improve PBE-like functionals?

  ChemRxiv · 2025-10-31

  articleOpen accessSenior author

  Correlated Orbital Theory (COT) provides an exact one-particle framework by imposing rigorous physical constraints on Kohn-Sham eigenvalues and, as a consequence, directly incorporates essential electron correlation into molecular orbitals. This approach paves the way toward a new class of approximations within Kohn–Sham Density Functional Theory (KS-DFT). However, since all existing Quantum Theory Project (QTP) functionals are derived from CAM-B3LYP, we pose the question: Can COT improve the hybrid versions of different exchange-correlation (XC) functionals as well? To that end, we explore two optimization strategies for adjusting the existing parameters within PBE0, TPSS0, and LC-PBE0: i) the ionization potential (IP) condition and ii) the HOMO–LUMO condition. In this sense, we critically assess how these functionals address the "Devil's Triangle" of KS-DFT: self-interaction error, integer discontinuity, and one-particle spectra. We further examine how the COT influences the description of two challenging properties, charge transfer and reaction barrier heights. Overall, enforcing both COT conditions systematically enhances the performance of functionals within the PBE family, although the description of reaction barriers still leaves room for improvement.

  PublisherDOI

• cQTP25: A New Exchange-Correlation Functional for Core-Electron Ionization Energy

  ChemRxiv · 2025-08-12

  preprintOpen access

  We present a new exchange-correlation (XC) functional inspired by Correlated Orbital Theory (COT), and designed to enhance the accuracy of core-electron ionization energy predictions as measured by X-ray photoelectron spectroscopy (XPS). This functional, referred to as cQTP25, differs from other Quantum Theory Project (QTP) functionals by optimizing the range-separation parameters through a targeted restriction of the orbital space to core 1s electrons only. We benchmarked cQTP25 against a diverse set of XC functionals spanning multiple rungs of Jacob's ladder in Density Functional Theory (DFT). Performance was evaluated primarily using the relation $IP_{1s} = -\varepsilon_{1s}$, but for completeness, we also computed core ionization potentials using the $\Delta$DFT method. All calculations accounted for both non-relativistic and relativistic corrections. In general, regardless of the computational approach or test set, the results consistently show the same trend: cQTP25 delivers the best performance, followed closely by QTP00 and then QTP17.

  PublisherDOI

• EOM-CCSD calculation of metal K pre-edge spectra: 3d transition metal tetrachlorides

  The Journal of Chemical Physics · 2025-05-19 · 2 citations

  articleSenior author

  The metal K pre-edge spectra of 3d transition metal tetrachlorides (MCl4, M = Ti, Fe, Co, Ni, and Cu) are obtained using the equation of motion coupled cluster (EOM-CC) approach. These spectra are primarily influenced by two key contributions to the oscillator strength-the electric dipole and quadrupole transition moments-due to the possible mixing of 3d and 4p orbitals in transition metal atoms. The EOM-CC singles and doubles method incorporating a recently implemented formalism that includes all the second-order contributions to oscillator strength [i.e., beyond the customary dipole approximation, Park et al., J. Chem. Phys. 155, 094103 (2021)] provides a powerful tool for computing excitation energies and oscillator strengths. This approach enables accurate interpretation of experimental spectra and facilitates predictions when experimental data are unavailable. In the present study, we demonstrate how these new extensions to the EOM-CC method can be utilized to compute metal K pre-edge spectra and determine the orbital characteristics of MCl4 complexes.

  PublisherDOI

• cQTP25: A New Exchange-Correlation Functional for Core-Electron Ionization Energy

  ChemRxiv · 2025-08-25

  preprintOpen access

  We present a new exchange-correlation (XC) functional inspired by Correlated Orbital Theory (COT), and designed to enhance the accuracy of core-electron ionization energy predictions as measured by X-ray photoelectron spectroscopy (XPS). This functional, referred to as cQTP25, differs from other Quantum Theory Project (QTP) functionals by optimizing the range-separation parameters through a targeted restriction of the orbital space to core 1s electrons only. We benchmarked cQTP25 against a diverse set of XC functionals spanning multiple rungs of Jacob's ladder in Density Functional Theory (DFT). Performance was evaluated primarily using the relation $IP_{1s} = -\varepsilon_{1s}$, but for completeness, we also computed core ionization potentials using the $\Delta$DFT method. All calculations accounted for both non-relativistic and relativistic corrections. In general, regardless of the computational approach or test set, the results consistently show the same trend: cQTP25 delivers the best performance, followed closely by QTP00 and then QTP17.

  PublisherOA PDFDOI

• Benchmarking ionization potentials and electron affinities of potential photovoltaic molecules using DFT/QTP functionals and EOM-CC

  The Journal of Chemical Physics · 2025-11-04

  articleSenior author

  Accurate predictions of ionization potentials and electron affinities are essential for guiding the design of organic photovoltaic materials. In this study, we revisit a set of twenty molecules that have been explored in earlier studies and extend the analysis using our approaches: (1) CC theory in its ionization potentials (IPs)/electron affinities (EAs)-equation-of-motion (EOM)/coupled-cluster singles and doubles (CCSD) forms to offer a direct measure of IPs and EAs and (2) Kohn-Sham density functional theory (DFT) using the QTP family compared to a broad range of exchange-correlation functionals (from simple local density approximation/generalized gradient approximation forms through hybrid and range-separated variants). For consistency with prior calculations, one-shot G0W0 corrections are applied to each QTP result. To reduce the cost of coupled-cluster computations, we also investigate both standard and tailored frozen natural orbital (FNO) truncations. Our results confirm that local and semi-local DFT functionals exhibit significant errors, whereas global hybrids and range-separated hybrids offer improved accuracy. The QTP functionals stand out by matching or exceeding the performance of all other functionals. G0W0 on top of DFT starting points further refines orbital energies, bringing them into close agreement with coupled-cluster results. Tailored FNO truncations preserve coupled-cluster accuracy while reducing the virtual space by nearly half. Timing tests on anthracene demonstrate that QTP00 and G0W0@QTP00 workflows almost achieve coupled-cluster quality predictions in under a day, compared with week-long runtimes for full EA-EOM/CCSD.

  PublisherDOI

Recent grants

• ITR: Science and Software for Predictive Simulation of Chemo-Mechanical Phenomena in Real Materials

  NSF · $2.5M · 2003–2008

• US-France Cooperative Research: Electronic Spectroscopy and Photochemistry of Transition Metal Complexes Studied via Coupled-Cluster Calculations and Wavepacket Propagation

  NSF · $20k · 2004–2007

• Super instruction architecture for petascale computing.

  NSF · $40k · 2009–2013

Frequent coauthors

• Ajith Perera

  University of Florida

  109 shared

• S. Ajith Perera

  Friedrich Schiller University Jena

  101 shared

• Janet E. Del Bene

  Youngstown State University

  88 shared

• José Elguero

  Instituto de Química Médica

  55 shared

• Ibón Alkorta

  Instituto de Química Médica

  54 shared

• John D. W. Watts

  Corpus Christi College

  54 shared

• George D. Purvis

  University of Florida

  53 shared

• John F. Stanton

  University of Florida

  48 shared

Labs

• Rodney J. BartlettPI

Education

• PhD, Chemistry

  University of Florida

  1971

Awards & honors

• Humboldt Senior Research Award (2014)
• The Boys-Rahman Prize of the Royal Society of Chemistry (RSC…
• The Schrödinger Medal of the World Association of Theoretica…
• The American Chemical Society (ACS) award in Theoretical Che…
• The Florida ACS Award (2000)