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Citations since 2017
12 Research Items
I am broadly interested in Chemical Physics, Computational Mineralogy and Stable Isotope Geochemistry. I have experience in ab initio DFT studies of elemental and isotopic fractionation, reaction kinetics, partition function theory and transition state theory.
RATIONALE Carbonate clumped isotope analysis involves the reaction of carbonate minerals with phosphoric acid to release CO2 for measurement in a gas‐source isotope ratio mass spectrometer. Although the clumped isotope proxy is based on the temperature dependence of ¹³C‐¹⁸O bonding preference in the mineral lattice, which is captured in the product...
Rationale Phosphoric acid digestion of carbonate generates CO2 for stable oxygen and clumped isotope analysis using a gas source isotope ratio mass spectrometer. The initial step of digestion reaction is protonation of calcite while the product CO2 equilibrates with the system allowing further exchange of isotopes to various extents depending on th...
Rationale In ‘clumped isotope paleothermometry’ carbonates are reacted with anhydrous phosphoric acid to extract CO2 that carries the isotopic signature of the reacting carbonates, and the amount of clumping in the product CO2 is measured. Previous theoretical models for determining clumped isotopic fractionation in product CO2 during acid digesti...
Phosphoric acid digestion of carbonate generates CO2 for stable oxygen and clumped isotope analysis using gas source isotope ratio mass spectrometer. The initial step of digestion reaction is protonation of calcite while the product CO2 equilibrates with the system allowing further exchange of isotopes to various extents depending on the nature of...
Urey  and Bigeleisen & Mayer  used molecular partition function ratios to calculate the equilibrium constant of a chemical reaction to study the isotope exchange process in equilibrium. At that time, it was not possible to measure the energies of isotopic molecules relative to the completely dissociated energy states of the molecule, and prec...
The cover image is based on the Research Article Fractionation of stable oxygen and clumped isotopes during acid digestion of calcite in the presence of an external direct current electric field by Sanchita Banerjee et al., https://doi.org/10.1002/rcm.8921.
How to minimize the effect of impurities from surroundings supercell images on our model supercell? My concern is about the surrounding periodic supercell images where also the modeled impurity is present at same locations. I want to minimize the effects from those supercells only. I can use non pbc calculation in Gaussian09 or similar package but there may be convergence failure as the lattice is stable in pbc only. Another method is to put vacuum around the molecules in the supercell to reduce the interaction but that is taking more resource. Please suggest if there is any other way.
In frequency calculations in Gaussian09 using DFT-B3LYP and 6-311+G(d) functional and basis set, we know that scaling factor is applied to correct the obtained frequencies. But is there any printable error bar for frequency calculations?
After getting transition state of a reaction by ab initio method how can we verify the structure? Theoretically it is one negative frequency and irc. But how can I verify experimentally? Is there any experimental ts structure for acid- calcium carbonate reaction? Please help.
I used qst3 to find the transition state (to calculate the rate) and irc to find the reaction path. is there anything else can be done? like i want to know is it correct if the solid is a crystal and i use one dimer of the solid molecules as reactant along with one or two liquid molecules? and how can i do relaxation (exact key word in Gaussian?) of H+ from liquid/acid molecule on the crystal surface containing 6 to 10 molecules?
I tried with Gaussian09 taking 1 CaCO3 and 1 H3PO4 molecule as input and got a combined structure having all atoms. I could not find how a single molecule of ionic crystal like CaCO3 can be input in G09. So i used single covalent bond between Ca++ and CO3--. Hence my calculation is wrong. Please inform how to input ionic molecule and how to find transition state of this reaction.
CaCO3+H3PO4= (Transition state)= CaHPO4+ H2CO3= CaHPO4+ CO2+ H2O