# Carlos Simmerling
Carlos L. Simmerling is a computational structural biologist at [Stony Brook University](https://www.edgepedia.org/stony-brook-university), where he is Marsha Laufer Professor of Physical and Quantitative Biology in the Department of Chemistry and a Fellow of the American Chemical Society.[1](https://www.stonybrook.edu/commcms/chemistry/people/faculty_profiles/simmerling-carlos.php) He is known for developing widely used protein force fields (mathematical model of forces between atoms in simulation) for the Amber molecular simulation package, including ff99SB, ff14SB, and ff19SB, and for a 2002 simulation in which a small protein folded from an extended chain to a structure within 0.97 Å of experiment.[2](https://dasher.wustl.edu/chem430/labs/lab-07/jacs-124-11258-02.pdf) His laboratory studies how dynamic structural changes drive the behavior of proteins and nucleic acids, and develops new methods for simulating conformational change and for validating molecular mechanics force fields.[1](https://www.stonybrook.edu/commcms/chemistry/people/faculty_profiles/simmerling-carlos.php)
| Fact | Detail |
|---|---|
| Field | Computational structural biology; biomolecular molecular dynamics[1](https://www.stonybrook.edu/commcms/chemistry/people/faculty_profiles/simmerling-carlos.php) |
| Signature work | ff14SB (JCTC 2015)[4](https://pubs.acs.org/doi/full/10.1021/acs.jctc.5b00255) and ff19SB (JCTC)[5](https://pubs.acs.org/doi/pdf/10.1021/acs.jctc.9b00591) Amber protein force fields |
| Honor | Fellow of the American Chemical Society[1](https://www.stonybrook.edu/commcms/chemistry/people/faculty_profiles/simmerling-carlos.php) |
## Education and career
Simmerling earned a B.A. in chemistry in 1991 and a Ph.D. in chemistry in 1994 at the University of Illinois at Chicago, working with Ron Elber.[3](https://static1.squarespace.com/static/5e7fd5f8b4495743110907de/t/6153666e97c58418d492d311/1632855663255/Simmerling.CV.Oct2021.pdf) He then spent 1994 to 1998 as a postdoctoral researcher with Peter Kollman in the Department of Pharmaceutical Chemistry at the [University of California, San Francisco](https://www.edgepedia.org/university-of-california-san-francisco).[3](https://static1.squarespace.com/static/5e7fd5f8b4495743110907de/t/6153666e97c58418d492d311/1632855663255/Simmerling.CV.Oct2021.pdf)
## Representative work
His 2002 paper in the [Journal of the American Chemical Society](https://www.edgepedia.org/journal-of-the-american-chemical-society) reported an all-atom, fully unrestrained folding simulation of a stable protein, the 20-residue Trp-cage peptide TC5b.[2](https://dasher.wustl.edu/chem430/labs/lab-07/jacs-124-11258-02.pdf) Starting only from the amino acid sequence in an extended conformation, using the Amber ff99 force field with refit backbone parameters and a Generalized Born solvation model, the simulation reached a predicted structure with a 0.97 Å C-alpha root-mean-square deviation and 1.4 Å over all heavy atoms from the experimental structure.[2](https://dasher.wustl.edu/chem430/labs/lab-07/jacs-124-11258-02.pdf) The work was done at the Center for Structural Biology and Department of Chemistry of the [State University of New York](https://www.edgepedia.org/state-university-of-new-york) at Stony Brook.[6](https://pubmed.ncbi.nlm.nih.gov/12236726/)
The force-field line continued in 2006, when limitations of the earlier ff94 model, such as over-stabilization of alpha-helices, led to the ff99SB parameter set, which refit backbone dihedral parameters against quantum-mechanical energies of glycine and alanine tetrapeptides and improved the balance of secondary structure elements.[7](http://folding.cnsm.csulb.edu/ffamber/pdfs/simmerling_amber99sb_2006proteins.pdf) In 2015, ff14SB performed a complete refit of all amino acid side chain dihedral parameters, which had been carried over from ff94, using multidimensional dihedral scans to improve transferability; average errors in relative conformational energies fell under 1.0 kcal/mol compared with quantum mechanics, a 35% reduction from ff99SB.[4](https://pubs.acs.org/doi/full/10.1021/acs.jctc.5b00255)
ff19SB, published in 2019, addressed the remaining weakness: the shared backbone treatment across amino acids. It fit coupled Φ/ψ parameters for all 20 amino acids against the entire two-dimensional quantum-mechanical energy surface in solution, and was validated with roughly 5 milliseconds of explicit-solvent molecular dynamics, better reproducing amino-acid-specific Ramachandran maps and helical propensities.[5](https://pubs.acs.org/doi/pdf/10.1021/acs.jctc.9b00591)
## Force-field development and the Amber project
The "SB" designation of his force fields reflects their Stony Brook origin.[1](https://www.stonybrook.edu/commcms/chemistry/people/faculty_profiles/simmerling-carlos.php) His laboratory also develops implicit-solvent water models for Amber.[3](https://static1.squarespace.com/static/5e7fd5f8b4495743110907de/t/6153666e97c58418d492d311/1632855663255/Simmerling.CV.Oct2021.pdf)
His laboratory's work beyond force fields studies the biophysics of changes in [protein tertiary structure](https://www.edgepedia.org/protein-tertiary-structure) during folding, the interactions that drive them, and how they are modified in disease or drug resistance.[8](https://www.simmerlinglab.org/) An NSF award from the Chemical Theory, Models and Computational Methods program supports continued force-field improvement, with three aims: fitting backbone energetics to high-level quantum-mechanical calculations in solution, expanding the Amber parameter library to non-standard amino acids, and addressing weaknesses in short-range van der Waals interactions; the resulting models are distributed freely through Amber.[9](https://researchconnect.stonybrook.edu/en/projects/improving-the-accuracy-of-the-amber-force-field-for-biomolecular-/)
## Independent benchmarks
Independent assessments place the SB force fields in context. A 2021 comparative study found that ff19SB combined with the [OPC water model](https://www.edgepedia.org/opc-water-model) gave the best prediction of weak dimerization of a soluble protein, while [CHARMM36m](https://www.edgepedia.org/charmm36m) predicted residue-wise alpha-helical propensities slightly better; the same study confirmed that ff14SB with TIP3P over-stabilizes aggregates and secondary structure, and concluded that the claimed force-field improvements are real but that a right balance between noncovalent attraction and repulsion has not yet been reached.[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC8120800/) A 2022 spectroscopic benchmark of Ramachandran distributions found that a Gaussian model fitted to experiment outperformed all four tested MD force fields, including ff19SB, by an order of magnitude, though ff19SB accounted for residue-specific polyproline II content better than the other three.[11](https://pubs.rsc.org/en/content/articlelanding/2022/cp/d1cp05069a) The ff19SB authors themselves reported that ff14SB carries an inherent underestimation of helicity, inexactly compensated by the TIP3P water model's bias toward overly compact structures, and recommended pairing ff19SB with a more accurate water model such as OPC.[5](https://pubs.acs.org/doi/pdf/10.1021/acs.jctc.9b00591)
## Recent work
In 2024, Simmerling was corresponding author on phosaa14SB and phosaa19SB, updated Amber parameters for the side chains of the most common phosphorylated amino acids, trained against quantum-mechanical reference data following the ff14SB approach and validated against experiment, with versions compatible with both ff14SB and ff19SB.[12](https://www.osti.gov/pages/servlets/purl/2448262) A 2025 review, "Recent Developments in Amber Biomolecular Simulations," appeared in the Journal of Chemical Information and Modeling.[13](https://www.csauthors.net/carlos-simmerling/)
## References
1. [Carlos Simmerling | Department of Chemistry, Stony Brook University](https://www.stonybrook.edu/commcms/chemistry/people/faculty_profiles/simmerling-carlos.php)
2. [All-Atom Structure Prediction and Folding Simulations of a Stable Protein (full text)](https://dasher.wustl.edu/chem430/labs/lab-07/jacs-124-11258-02.pdf)
3. [Carlos Simmerling CV, October 2021](https://static1.squarespace.com/static/5e7fd5f8b4495743110907de/t/6153666e97c58418d492d311/1632855663255/Simmerling.CV.Oct2021.pdf)
4. [ff14SB: Improving the Accuracy of Protein Side Chain and Backbone Parameters from ff99SB](https://pubs.acs.org/doi/full/10.1021/acs.jctc.5b00255)
5. [ff19SB: Amino-Acid-Specific Protein Backbone Parameters Trained against Quantum Mechanics Energy Surfaces in Solution](https://pubs.acs.org/doi/pdf/10.1021/acs.jctc.9b00591)
6. [All-atom structure prediction and folding simulations of a stable protein (PubMed)](https://pubmed.ncbi.nlm.nih.gov/12236726/)
7. [Comparison of multiple Amber force fields and development of improved protein backbone parameters (Proteins, 2006)](http://folding.cnsm.csulb.edu/ffamber/pdfs/simmerling_amber99sb_2006proteins.pdf)
8. [Simmerling Lab](https://www.simmerlinglab.org/)
9. [Improving the Accuracy of the Amber Force Field for Biomolecular Simulation (NSF award)](https://researchconnect.stonybrook.edu/en/projects/improving-the-accuracy-of-the-amber-force-field-for-biomolecular-/)
10. [Assessment of transferable forcefields for protein simulations (2021)](https://pmc.ncbi.nlm.nih.gov/articles/PMC8120800/)
11. [Do molecular dynamics force fields accurately model Ramachandran distributions of amino acid residues in water? (2022)](https://pubs.rsc.org/en/content/articlelanding/2022/cp/d1cp05069a)
12. [phosaa14SB and phosaa19SB: Updated Amber Force Field Parameters for Phosphorylated Amino Acids](https://www.osti.gov/pages/servlets/purl/2448262)
13. [Carlos Simmerling (csauthors)](https://www.csauthors.net/carlos-simmerling/)
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*Topic: Encyclopedia › Life and health › Life and health scientists › Life scientists › Researchers in structural biology, biochemistry, and biophysics*
*Initially written Sep 21, 2026 · Reviewed: Sep 25, 2026 · Edited: Sep 25, 2026; Oct 15, 2026 · Last review: Sep 25, 2026*
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