Research Interests

Excited state orbital optimization.
Linear response aproaches like Time-Dependent Density Functional Theory (TDDFT) or equation of motion coupled cluster (EOM-CC) are susceptible to catastrophic failure for problems where excited state orbitals differ considerably from ground state ones (such as in core or double excitations, or charge-transfer states in TDDFT). Explicit optimization of excited state orbitals is on the other hand quite challenging, as excited states are energy saddle points in orbital space and so solvers are quite prone to “variational collapse” down to a minimum like the ground state instead. We have recently developed a way to mitigate this problem for any arbitrary quantum chemical method via minimizing the square of the energy gradient instead. This Square Gradient Minimization (SGM) approach costs only 2-3 times as much as ground state optimization (per iteration) and can be combined with modern density functionals to yield very high accuracy for challenging problems. 

Development and Assessment of Density Functionals
Historically, functional development had mostly focused on improving prediction of energetics. It has been suggested (Science 355.6320 (2017): 49-52.) that this approach has led to overparametrization of functionals, leading to worse predictions of non-energetic properties like densities.  I am currently investigating the ability of current functionals in predicting density and electrical response properties like polarizibilities, with the ultimate objective of using this information to develop functionals that do not sacrifice prediction of density and related properties merely for the sake of improving energetics .

Development of Selected CI techniques
There has been a recent renaissance in selected configuration interaction (CI) methods on account of the development of Adaptive Sampling CI (ASCI), Heat-bath CI (HCI), Adaptive CI (ACI) etc. I am working with Norm Tubman in the Whaley Group and Daniel Levine on developing and optimizing the ASCI method further, along with applying it to interesting systems.

Collaborations with Experimentalists
I enjoy applying quantum chemistry methods to solve problems experimentalists encounter in their wet (or not so wet) lab research. I have worked on quite varied areas like crossed molecular beams, calculating spin-spin couplings in MOFs, stereoselective synthesis and  predicting UV/Vis spectra.
Feel free to drop me a line if you are an experimentalist who wants to pick a theorist’s brain. I have far too many active commitments to take on a new collaboration at the moment, but I do enjoy pointing people towards (what I think is ) the right direction.

Publications

First or Second Author (* indicates equal contributions)

1. Orbital Optimized Density Functional Theory for Electronic Excited States. (arxiv)
   Hait D., Head-Gordon M.
   Journal of Physical Chemistry Letters 2021 12 (19), 4517–4529.
2. Two-Coordinate Iron(I) Complexes on the Edge of Stability: Influence of Dispersion and Steric Effects. 
   Witzke R.J., Hait D., Head-Gordon M., Tilley T.D.
   Organometallics 2021 40 (11), 1758–1764.
3. Too big, too small, or just right? A benchmark assessment of density functional theory for predicting the spatial extent of the electron density of small chemical systems. (arxiv)
   Hait D.*, Liang Y.H.*, Head-Gordon M.
   Journal of Chemical Physics 2021 154 (7), 074109.
4. Third-Order Møller–Plesset Theory Made More Useful? The Role of Density Functional Theory Orbitals. (arxiv)
   Rettig A.*, Hait D.*, Bertels L.W., and Head-Gordon M.
   Journal of Chemical Theory and Computation 2020 16 (12), 7473–7489.
5. Accurate prediction of core-level spectra of radicals at density functional theory cost via square gradient minimization and recoupling of mixed configurations. (arxiv)
   Hait D., Haugen E.A., Yang Z., Oosterbaan K.J., Leone S.R., Head-Gordon M.
   Journal of Chemical Physics 2020 153 (13), 134108.
6. Bimetallic mechanismfor alkyne cyclotrimerization with a two-coordinate Fe precatalyst. 
   Witzke R.J., Hait D., Chakarawet K., Head-Gordon M., Tilley T.D.
   ACS Catalysis 2020 10(14), 7800-7807.
7. CASSCF with Extremely Large Active Spaces Using the Adaptive Sampling Configuration Interaction Method. (arXiv)
   Levine D.S., Hait D., Tubman N.M., Lehtola S., Whaley K.B., Head-Gordon M.
   Journal of Chemical Theory and Computation 2020 16 (4), 2340-2354.
8. Excited state orbital optimization via minimizing the square of the gradient: General approach and application to singly and doubly excited states via density functional theory. (arxiv)
   Hait D., Head-Gordon M.
   Journal of Chemical Theory and Computation 2020 16 (3), 1699-1710.
9. Highly Accurate Prediction of Core Spectra of Molecules at Density Functional Theory Cost: Attaining sub eV Error from a Restricted Open-Shell Kohn-Sham Approach. (arxiv)
   Hait D., Head-Gordon M.
   Journal of Physical Chemistry Letters 2020 11 (3), 775-786.
10. Beyond the Coulson–Fischer point: characterizing single excitation CI and TDDFT for excited states in single bond dissociations. (arXiv)
    Hait D.*, Rettig A.*, Head-Gordon M.
    Physical Chemistry Chemical Physics 2019 21, 21761-21775.
11. What levels of coupled cluster theory are appropriate for transition metal systems? A study using near exact quantum chemical values for 3d transition metal binary compounds. (ChemRxiv)
    Hait D., Tubman N.M., Levine D.S., Whaley K.B., Head-Gordon M.
    Journal of Chemical Theory and Computation 2019 15 (10), 5370-5385.
12. Chemoenzymatic Platform for Synthesis of Chiral Organofluorines Based on Type II Aldolases.
    Fang J., Hait D., Head-Gordon M., Chang M.C.Y.
    Angewandte Chemie International Edition 2019, 58 (34), 11841-11845.
13. Well-behaved versus ill-behaved density functionals for single bond dissociation: Separating success from disaster functional by functional for stretched H₂ (pdf, arxiv)
    Hait D.*, Rettig A.*, Head-Gordon M.
    Journal of Chemical Physics 2019 150 (9), 094115.
14. Delocalization Errors in Density Functional Theory are Essentially Quadratic in Fractional Occupation Number (arXiv)
    Hait D., Head-Gordon M.
    Journal of Physical Chemistry Letters 2018 9 (21), 6280–6288.
15. How Accurate Are Static Polarizability Predictions from Density Functional Theory? An Assessment over 132 Species at Equilibrium Geometry (ChemRxiv)
    Hait D., Head-Gordon M.
    Physical Chemistry Chemical Physics 2018 20 (30), 19800-19810.
16. xDH double hybrid functionals can be qualitatively incorrect for non-equilibrium geometries: Dipole moment inversion and barriers to radical-radical association using XYG3 and XYGJ-OS (pdf, arxiv)
    Hait D., Head-Gordon M.
    Journal of Chemical Physics 2018 148 (17), 171102.
17. How accurate is density functional theory at predicting dipole moments? An assessment using a new database of 200 benchmark values (arxiv)
    Hait D., Head-Gordon M.
    Journal of Chemical Theory and Computation 2018 14 (4), 1969–1981.

Contributing Author

1. Revealing the nature of electron correlation in transition metal complexes with symmetry breaking and chemical intuition. (ChemRxiv)
   Shee J., Loipersberger M., Hait D., Lee J., Head-Gordon M.
   Journal of Chemical Physics 2021 154 (19),  194109.
2. Electron–Nuclear Dynamics Accompanying Proton-Coupled Electron Transfer. 
   Yoneda Y. et.al.
   Journal of the American Chemical Society 2021 143 (8), 3104-3112.
3. The Ground State Electronic Energy of Benzene (arxiv)
   Eriksen J.J. et.al.
   Journal of Physical Chemistry Letters 2020  11, 8922-8929.
4. Generalized single excitation configuration interaction: an investigation into the impact of the inclusion of non-orthogonality on the calculation of core-excited states. (ChemRxiv)
   Oosterbaan K.J., White A.F.,  Hait D., Head-Gordon M.
   Physical Chemistry Chemical Physics 2020 22, 8182-8192.
5. Modern Approaches to Exact Diagonalization and Selected Configuration Interaction with the Adaptive Sampling CI Method (arXiv)
   Tubman N.M., Freeman C.D., Levine D.S., Hait D., Head-Gordon M., Whaley K.B.
   Journal of Chemical Theory and Computation 2020 16 (4), 2139–2159.
6. Bimolecular Reaction Dynamics in the Phenyl–Silane System: Exploring the Prototype of a Radical Substitution Mechanism (ChemRxiv)
   Lucas M., Thomas A.M., Yang T., Kaiser R.I. , Mebel A.M., Hait D., Head-Gordon M.
   Journal of Physical Chemistry Letters 2018 9 (17), 5135-5142.

See CV for publications related to work prior to Berkeley.