**Position:** Graduate Student**Office:** 48 Gilman Hall**Email:** diptarka AT berkeley.edu**CV** **Education**S.B. in Chemistry and Physics (2016

**)**

Massachusetts Institute of Technology

Advisor: Professor Troy Van Voorhis

**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

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 Author**** (* indicates equal contributions)**

- 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. - 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. - 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. - 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. - Well-behaved versus ill-behaved density functionals for single bond dissociation: Separating success from disaster functional by functional for stretched H
_{2}(pdf, arxiv)**Hait D.***, Rettig A.*, Head-Gordon M.*Journal of Chemical Physics***2019**150 (9), 094115. - 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. - 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. - 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. - 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.

**Other Publications**

- Bimetallic mechanismfor alkyne cyclotrimerization with a two-coordinate Fe precatalyst

Witzke R.J.,Chakarawet K., Head-Gordon M., Tilley T.D.**Hait**D.,*ACS Catalysis***2020**. - 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. - 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. - 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. - 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. - 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.