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Dr Aron Cohen

Portrait of ajc54

Our research focuses on the understanding and development of electronic structure methods, particularly that of density functional theory (DFT). DFT is an important computational tool with widespread use throughout many areas of chemistry and physics. The beauty of DFT is that it is an exact theory, yet conceptually and computationally simple. However there is one term that has to be approximated, the exchange-correlation functional, and the validity of any DFT calculation relies completely upon it.

Our work focuses on understanding and improving currently used approximations (such as LDA or B3LYP). It has been understood in the literature that these functionals can suffer from a delocalisation error, as exemplified by the incorrect dissociation of H2+, and a static correlation error, as shown by the errors in stretching of closed-shell H2. We now understand that these two errors should not be considered separately but rather as just two symptoms that come from the violation of a unified exact condition. The understanding of this exact condition of the exchange-correlation functional, even for a system as simple as the hydrogen atom, has lead to a much deeper understanding of the derivative discontinuity, strongly correlated systems and Mott insulators.

We are beginning to explore the consequences of this and other rationales to address many of the outstanding problems of DFT. We are currently interested in investigating and understanding the effects of the exchange-correlation functional for many systems including organic reactions in chemistry, excitation energies of molecules, polarisabilities of polymers and band-gaps and magnetic properties of solids.

Selected Publications

Challenges for Density Functional Theory. Aron J. Cohen, Paula Mori-Sánchez and Weitao Yang Chem. Rev. 112, 289 (2012)

Revealing Noncovalent Interactions. Erin R. Johnson, Shahar Keinan, Paula Mori-Sánchez, Julia Contreras-Garcia, Aron J. Cohen and Weitao Yang J. Am. Chem. Soc. 132, 6498 (2010)

Discontinuous Nature of the Exchange-Correlation Functional in Strongly Correlated Systems. Paula Mori-Sánchez, Aron J. Cohen and Weitao Yang Phys. Rev. Lett. 102, 066403, (2009)

Insights into current limitations of density functional theory. Aron J. Cohen, Paula Mori-Sánchez and Weitao Yang Science 321, 792, (2008)

Localization and delocalization errors in density functional theory and implications for band-gap prediction. Paula Mori-Sánchez, Aron J. Cohen and Weitao Yang Phys. Rev. Lett. 100, 146401, (2008)

 

Publications

Dramatic changes in electronic structure revealed by fractionally charged nuclei
AJ Cohen, P Mori-Sanchez – The Journal of Chemical Physics (2014) 140, 044110
Extension of many-body theory and approximate density functionals to fractional charges and fractional spins
W Yang, P Mori-Sánchez, AJ Cohen – The Journal of chemical physics (2013) 139, 104114
Derivative discontinuity, bandgap and lowest unoccupied molecular orbital in density functional theory.
W Yang, AJ Cohen, P Mori-Sánchez – The Journal of chemical physics (2012) 136, 204111
Analytical evaluation of Fukui functions and real-space linear response function
W Yang, AJ Cohen, F De Proft, P Geerlings – The Journal of chemical physics (2012) 136, 144110
Failure of the random-phase-approximation correlation energy
P Mori-Sanchez, AJ Cohen, WT Yang – Physical Review A (2012) 85, ARTN 042507
Optimized effective potential for calculations with orbital-free potential functionals
D Peng, B Zhao, AJ Cohen, X Hu, W Yang – Molecular Physics (2012) 110, 925
Challenges for density functional theory
AJ Cohen, P Mori-Sánchez, W Yang – Chem Rev (2012) 112, 289
Improving Band Gap Prediction in Density Functional Theory from Molecules to Solids
X Zheng, AJ Cohen, P Mori-Sánchez, X Hu, W Yang – Phys Rev Lett (2011) 107, 026403
Revealing noncovalent interactions.
ER Johnson, S Keinan, P Mori-Sánchez, J Contreras-García, AJ Cohen, W Yang – Journal of the American Chemical Society (2010) 132, 6498
Evaluation of Coupled Perturbed and Density Functional Methods of Computing the Parity-Violating Energy Difference between Enantiomers
AJ MacDermott, GO Hyde, AJ Cohen – Orig Life Evol Biosph (2009) 39, 439
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Research Group

Research Interest Group

Telephone number

01223 763874 (shared)

Email address

ajc54@cam.ac.uk