SAIKAT MUKHERJEE | Aix-Marseille Université (original) (raw)

Papers by SAIKAT MUKHERJEE

Recent experimental work revealed that the lifetime of the S3 state of protonated 7-azaindole is ... more Recent experimental work revealed that the lifetime of the S3 state of protonated 7-azaindole is about ten times slower than that of protonated 6-azaindole. We simulated the nonradiative decay pathways of these molecules using trajectory surface hopping dynamics after photoexcitation into S3 to elucidate the reason for this difference. Both isomers mainly follow a common pp* relaxation pathway involving multiple state crossings while coming down from S3 to S1 in the subpicosecond time scale. However, the simulations reveal that the excited-state topographies are such that while the 6-isomer can easily access the region of nonadiabatic transitions, the internal conversion of the 7-isomer is delayed by a pre-Dewar bond formation with a boat conformation.

Physical Chemistry Chemical Physics

Nonadiabatic surface hopping simulations demonstrate that the lifetime of the S3 state of protona... more Nonadiabatic surface hopping simulations demonstrate that the lifetime of the S3 state of protonated 7-azaindole is much longer than that of protonated 6-azaindole due to a puckered pre-Dewar structure in the S3 minimum of the 7-isomer.

The problem associated with the zero-point energy (ZPE) leak in classical trajectory calculations... more The problem associated with the zero-point energy (ZPE) leak in classical trajectory calculations is well known. Since ZPE is a manifestation of the quantum uncertainty principle, there are no restrictions on energy during the classical propagation of nuclei. This phenomenon can lead to unphysical results, such as forming products without the ZPE in the internal vibrational degrees of freedom (DOFs). The ZPE leakage also permits reactions below the quantum threshold for the reaction. We have developed a new Hessian-free method, inspired by the Lowe-Andersen thermostat model, to prevent energy dipping below a threshold in the local-pair (LP) vibrational DOFs. The idea is to pump the leaked energy to the corresponding local vibrational mode, taken from the other vibrational DOFs. We have applied the new correction protocol on the ab initio ground-state molecular dynamics simulation of the water dimer (H20)2, which dissociates due to unphysical ZPE spilling from the high-frequency OH m...

Annual Review of Physical Chemistry, 2021

The workability of beyond Born-Oppenheimer theory to construct diabatic potential energy surfaces... more The workability of beyond Born-Oppenheimer theory to construct diabatic potential energy surfaces (PESs) of a charge transfer atom-diatom collision process has been explored by performing scattering calculations to extract accurate integral cross sections (ICSs) and rate constants for comparison with most recent experimental quantities. We calculate non-adiabatic coupling terms among the lowest three singlet states of H + 3 system (1 1 A , 2 1 A , and 3 1 A ) using MRCI level of calculation and solve the adiabatic-diabatic transformation equation to formulate the diabatic Hamiltonian matrix of the same process [S. Mukherjee et al., J. Chem. Phys. 141, 204306 (2014)] for the entire region of nuclear configuration space. The nonadiabatic effects in the D + + H 2 reaction has been studied by implementing the coupled 3D time-dependent wave packet formalism in hyperspherical coordinates [S. Adhikari and A. J. C. Varandas, Comput. Phys. Commun. 184, 270 ] with zero and non-zero total angular momentum (J) on such newly constructed accurate (ab initio) diabatic PESs of H + 3 . We have depicted the convergence profiles of reaction probabilities for the reactive non-charge transfer, non-reactive charge transfer, and reactive charge transfer processes for different collisional energies with respect to the helicity (K) and total angular momentum (J) quantum numbers. Finally, total and state-to-state ICSs are calculated as a function of collision energy for the initial rovibrational state (v = 0, j = 0) of the H 2 molecule, and consequently, those quantities are compared with previous theoretical and experimental results. Published by AIP Publishing. [http://dx.

A thorough investigation has been performed for electronic structure, topological effect, and nuc... more A thorough investigation has been performed for electronic structure, topological effect, and nuclear dynamics of NO2 molecule, where the adiabatic potential energy surfaces (PESs), conical intersections between the ground (X2A1) and the first excited state (A2B2), and the corresponding
non-adiabatic coupling terms between those states are recalculated [Chem. Phys. 416, 11 (2013)] to achieve enough accuracy in dynamics. We employ beyond Born-Oppenheimer theory for these two state sub-Hilbert space to carry out adiabatic to diabatic transformation (ADT) to obtain the
ADT angles and thereby, to construct single-valued, smooth, and continuous diabatic PESs. The analytic expressions for the adiabatic PESs and ADT angles are provided to represent a two-state three-mode diabatic Hamiltonian of NO2 for performing nuclear dynamics to calculate the photoelectron
spectra of its anion. It appears that not only Jahn-Teller type coupling but also Renner-Teller interaction contributes significantly on the overall spectrum. The coupling between the electronic states (X2A1 and A2B2) of NO2 is essentially through the asymmetric stretching mode, where the
functional form of such interaction is distinctly symmetric and non-linear.

This article continues a previous study (Int. J. Quantum Chem. 114, 1645 (2014)) inwhich is prese... more This article continues a previous study (Int. J. Quantum Chem. 114, 1645 (2014)) inwhich is presented a
theory that discusses the possibility to induce a novel field – to be called molecular field – via the interaction
of an external electro-magnetic (EM) field and a molecular system.Assuming the molecular systemismade
up of two coupled adiabatic states the theory leads fromthree time-space curl equations
and one time-space divergence equation to a set of decoupled wave equations usually encountered
for fields. In the present study, wave equations are derived for an external field having two features:
(1) the field intensity is relatively high enough; (2) the duration of the interaction is short enough.
For this situation, the study reveals that the just mentioned interaction creates two fields that
coexist within a molecule: one is just a scalar EM field essentially identical to the external EM field
and the other, a vectorial field, produced by the non-adiabatic coupling terms. In addition, we
mention that the wave velocities related to these two fields are identical to the wave velocity, c, of
the external EM field.

We calculate the adiabatic Potential Energy Surfaces (PESs) and the Non-Adiabatic Coupling Terms ... more We calculate the adiabatic Potential Energy Surfaces (PESs) and the Non-Adiabatic Coupling Terms (NACTs) for the three lowest singlet states of H3+ in hyperspherical coordinates as functions of hyperangles (θ and φ) for a grid of fixed values of hyperradius (1.5 ≤ ρ ≤ 20 bohrs) using the MRCI level of methodology employing ab initio quantum chemistry package (MOLPRO). The NACT between the ground and the first excited state translates along the seams on the θ − φ space, i.e., there are six Conical Intersections (CIs) at each θ (60◦ ≤ θ ≤ 90◦) within the domain, 0 ≤ φ ≤ 2π. While transforming the adiabatic PESs to the diabatic ones, such surfaces show up six crossings along those seams. Our beyond Born-Oppenheimer approach could incorporate the effect of NACTs accurately
and construct single-valued, continuous, smooth, and symmetric diabatic PESs. Since the location of CIs and the spatial amplitudes of NACTs are most prominent around ρ = 10 bohrs, generally only those results are depicted.

We report here on the two lowest, rigorous-accurate diabatic potential energy surfaces (PES), for... more We report here on the two lowest, rigorous-accurate diabatic potential energy surfaces (PES), for the F + H 2 system, as calculated by including the two dominant topological effects of this system at the low energy region, namely, the Jahn−Teller effect and the Renner−Teller effect. Both effects were treated in the most rigorous way as demanded by the Born− Oppenheimer approach. No approximations were made, and in those cases where convergence was required, it was satisfied. In other words, convergence was attained in all situations. The numerical part that includes the calculation of the two lowest ab initio adiabatic PESs and the corresponding nonadiabatic coupling terms (NACTs) was carried out using the MOLPRO program. The required diabatic potentials are calculated by employing these ab initio adiabatic PESs and the corresponding adiabatic-to-diabatic angles as obtained employing the above-mentioned ab initio NACTs. The relevance of these Renner−Teller/Jahn−Teller diabatic potentials is studied by comparing the dressed-lowest ab initio adiabatic PES and the one formed by diagonalizing the dressed-diabatic 2 × 2 potential matrix. The dressed-potentials are calculated employing the vib-rotational manifold derived for each of the three surfaces, namely, the lowest adiabatic potential and the two diabatic ones. This kind of study was recently recommended by Herschbach (Mol. Phys. 2010, 108, 1133) as a "blessed-practice" for the relevance of any PES. In the present case significant differences were revealed between the two types of dressed-adiabatic PESs, eventually, indicating that the lowest, ab initio PES (due to the Born− Oppenheimer approximation) is not adequate for low energy processes.

We follow a suggestion by Herschbach (Mol. Phys. 2010, 108, 1133) and compare dressed potentials ... more We follow a suggestion by Herschbach (Mol. Phys. 2010, 108, 1133) and compare dressed potentials to get insight regarding the low-energy dynamics (e.g., cold reaction) taking place in molecular systems. In this particular case we are interested in studying the effect of topological effects on the interacting atoms. For this purpose we consider dressed adiabatic and adiabatic-via-dressed diabatic potentials in the entrance channel of reactive systems. In a recent study of this kind for the F + H 2 system (J. Chem. Phys. 2012, 136, 054104), we revealed that a single Jahn−Teller conical intersection is expected to have only a mild effect on the dynamics. This fact implies that the Born−Oppenheimer approximation is expected to be valid for this system at least for low enough energies. In the present article this study is extended to include also the Renner-Teller effect as produced by the two lower degenerate Π states. As a result we consider three electronic states which enforce the use of the adiabatic-to-diabatic transformation (ADT) matrix A. The results indicate that the topological effects as produced by the extended Renner/Teller-Jahn/Teller system are strong to the level that, most likely, abolishes the Born−Oppenheimer approximation for this system, all this in contrast to our previous findings (see above publication).

We calculate the adiabatic Potential Energy Surfaces (PESs) and the Non -Adiabatic Coupling Terms... more We calculate the adiabatic Potential Energy Surfaces (PESs) and the Non -Adiabatic Coupling Terms (NACTs) for the excited electronic states (2 2 E and 1 2 A 1 ) of N a3 cluster at the MRCI level by using ab initio quantum chemistry package (MOLPRO), where the NACTs are adapted with Molecular Symmetry (MS) by employing appropriate Irreducible Representations (IREPs). Such terms are incorporated into the Adiabatic to Diabatic Transformation (ADT) equations to obtain the ADT angles to construct the continuous, single -valued, symmetric and smooth 3 × 3 diabatic Hamiltonian matrix.

We perform four-dimensional (4D⊗2D) as well as six-dimensional (6D) quantum dynamics on a paramet... more We perform four-dimensional (4D⊗2D) as well as six-dimensional (6D) quantum dynamics on a parametrically time-and temperature-dependent effective Hamiltonian for D 2 (v, j)-Cu(111) system, where such effective potential has been derived through a mean-field approach between molecular degrees of freedom and surface modes with Bose-Einstein probability factor for their initial state distribution. We present the convergence of the theoretically calculated sticking probabilities employing 4D⊗2D quantum dynamics with increasing number of surface atoms as well as layers for rigid surface and the surface at a particular temperature, where the temperature-dependent sticking probabilities appear exclusively dictated by those surface modes directed along the Z-axis. The sticking and state-to-state transition probabilities obtained from 6D quantum dynamics are shown as a function of initial kinetic energy of the diatom at different surface temperature. Theoretically calculated sticking probabilities display the similar trend with the experimentally measured one.

Global potential energy surfaces of NO 2 Non-adiabatic coupling terms of NO 2 Jahn-Teller conical... more Global potential energy surfaces of NO 2 Non-adiabatic coupling terms of NO 2 Jahn-Teller conical intersections Renner-Teller conical intersections C 2v seam Ab initio calculation on NO 2 a b s t r a c t

Journal of Physical Chemistry A

We present the molecular symmetry (MS) adapted treatment of nonadiabatic coupling terms (NACTs) f... more We present the molecular symmetry (MS) adapted treatment of nonadiabatic coupling terms (NACTs) for the excited electronic states (22E′ and 12A1 ′) of Na3 cluster, where the adiabatic potential energy surfaces (PESs) and the NACTs are calculated at the MRCI level by using an ab initio quantum chemistry package (MOLPRO). The signs of the NACTs at each point of the configuration space (CS) are determined by employing appropriate irreducible representations (IREPs) arising due to MS group, and such terms are incorporated into the adiabatic to diabatic transformation (ADT) equations to obtain the ADT angles. Since those sign corrected NACTs and the corresponding ADT angles demonstrate the validity of curl condition for the existence of three-state (22E′ and 12A1 ′) sub-Hilbert space, it becomes possible to construct the continuous, single-valued, symmetric, and smooth 3 × 3 diabatic Hamiltonian matrix. Finally, nuclear dynamics has been carried out on such diabatic surfaces to explore whether our MS-based treatment of diabatization can reproduce the pattern of the experimental spectrum for system B of Na3 cluster.

Chemical Physics

We calculate the adiabatic potential energy surfaces (PESs) and the non-adiabatic coupling terms ... more We calculate the adiabatic potential energy surfaces (PESs) and the non-adiabatic coupling terms (NACTs) for the excited electronic states of K3 cluster by MRCI approach using MOLPRO. The NACTs are adapted with molecular symmetry to assign appropriate IREPs so that the elements of the Hamiltonian matrix are totally symmetric. We incorporate those NACTs into three-state adiabatic-to-diabatic transformation (ADT) equations to obtain ADT angles for constructing continuous, single-valued, smooth and symmetric diabatic Hamiltonian matrix, where its elements are fitted with analytic functions. Finally, we demonstrate
that the dressed diabatic and adiabatic-via-dressed diabatic PECs show prominent topological effect over dressed adiabatic curves.

Physical Chemistry Chemical Physics

Annual Review of Physical Chemistry, 2021

We calculate the adiabatic Potential Energy Surfaces (PESs) and the Non -Adiabatic Coupling Terms... more We calculate the adiabatic Potential Energy Surfaces (PESs) and the Non -Adiabatic Coupling Terms (NACTs) for the excited electronic states (2 2 E and 1 2 A 1 ) of N a3 cluster at the MRCI level by using ab initio quantum chemistry package (MOLPRO), where the NACTs are adapted with Molecular Symmetry (MS) by employing appropriate Irreducible Representations (IREPs). Such terms are incorporated into the Adiabatic to Diabatic Transformation (ADT) equations to obtain the ADT angles to construct the continuous, single -valued, symmetric and smooth 3 × 3 diabatic Hamiltonian matrix.

Journal of Physical Chemistry A

Chemical Physics