@article { ISI:000346385900016, title = {Relativistic equation-of-motion coupled-cluster method for the ionization problem: application to molecules}, journal = {Physical Review A}, volume = {90}, number = {6}, year = {2014}, month = {DEC}, pages = {Article No. 062501}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

We report the implementation of the four-component spinor relativistic equation-of-motion (EOM) coupled-cluster method within the single- and double-excitation approximation to calculate the ionization potential of molecules. We have applied this method to calculate vertical ionization potentials of the molecules XH (X = F, Cl, Br, I) along with Cl-2 and Br-2 in their closed-shell configuration. We have also presented intermediate results using the second-order many-body perturbation-theory level in the EOM framework to understand the role of electron correlation. All the calculated values are compared with the available experimental results. Our results are found to be in good agreement with sophisticated experiments, and relative deviation of less than 1\% is achieved for all the considered systems.

}, issn = {1050-2947}, doi = {10.1103/PhysRevA.90.062501}, author = {Pathak, Himadri and Sasmal, Sudip and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article { ISI:000360653900022, title = {Calculation of P,T-odd interaction constant of PbF using Z-vector method in the relativistic coupled-cluster framework}, journal = {Journal of Chemical Physics}, volume = {143}, number = {8}, year = {2015}, month = {AUG}, pages = {084119}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {

The effective electric field experienced by the unpaired electron in the ground state of PbF, which is a potential candidate in the search of electron electric dipole moment due to some special characteristics, is calculated using Z-vector method in the coupled cluster single-and double-excitation approximation with four component Dirac spinor. This is an important quantity to set the upper bound limit of the electron electric dipole moment. Further, we have calculated molecular dipole moment and parallel magnetic hyperfine structure constant (A(parallel to)) of Pb-207 in PbF to test the accuracy of the wavefunction obtained in the Z-vector method. The outcome of our calculations clearly suggests that the core electrons have significant contribution to the {\textquoteleft}{\textquoteleft}atom in compound{\textquoteright}{\textquoteright} properties. (C) 2015 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4929591}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article { ISI:000352195500001, title = {Implementation of the Z-vector method in the relativistic-coupled-cluster framework to calculate first-order energy derivatives: Application to the SrF molecule}, journal = {Physical Review A}, volume = {91}, number = {3}, year = {2015}, month = {MAR}, pages = {030503}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

The molecular dipole moment and magnetic hyperfine-structure constant demand an accurate wave function far from the nucleus and in the near nuclear region, respectively. We, therefore, employ the so-called Z-vector method in the domain of relativistic-coupled-cluster theory to calculate the first-order property of molecular systems in their open-shell ground-state configuration. The implemented method is applied to calculate the molecular dipole moment and parallel component of the magnetic hyperfine-structure constant of the SrF molecule. The results of our calculation are compared with the experimental and other available theoretically calculated values. We are successful in achieving good accordance with the experimental results. The result of our calculation of the molecular dipole moment is in the accuracy of similar to 0.5\%, which is clearly an improvement over the previous calculation based on the expectation value method in the four-component coupled-cluster framework [V. S. Prasannaa et al., Phys. Rev. A 90, 052507 (2014)]. Thus, it can be inferred that the Z-vector method can provide an accurate wave function in both the near and far nuclear region, which is evident from our calculated results.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.91.030503}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {42629, title = {Relativistic extended coupled cluster method for magnetic hyperfine structure constant}, journal = {Physical Review A}, volume = {91}, year = {2015}, month = {FEB}, pages = {Article No. 022512}, type = {Article}, doi = {10.1103/PhysRevA.91.022512}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {43584, title = {Calculation of hyperfine structure constants of small molecules using Z-vector method in the relativistic coupled-cluster framework}, journal = {Journal of Chemical Sciences}, volume = {128}, year = {2016}, month = {OCT}, pages = {1671-1675}, abstract = {The Z-vector method in the relativistic coupled-cluster framework is employed to calculate the parallel and perpendicular components of the magnetic hyperfine structure constant of a few small alkaline earth hydrides (BeH, MgH, and CaH) and fluorides (MgF and CaF). We have compared our Z-vector results with the values calculated by the extended coupled-cluster (ECC) method reported in Phys. Rev. A 91 022512 (2015). All these results are compared with the available experimental values. The Z-vector results are found to be in better agreement with the experimental values than those of the ECC values.}, doi = {10.1007/s12039-016-1174-1}, author = {Sasmal, Sudip and Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article { ISI:000377497000004, title = {Relativistic coupled-cluster study of RaF as a candidate for the parity- and time-reversal-violating interaction}, journal = {Physical Review A}, volume = {93}, number = {6}, year = {2016}, month = {JUN}, pages = {062506}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

We have employed both the Z-vector method and the expectation-value approach in the relativistic coupled-cluster framework to calculate the scalar-pseudoscalar (S-PS) P, T-odd interaction constant W-s and the effective electric field E-eff experienced by the unpaired electron in the ground electronic state of RaF. Further, the magnetic hyperfine structure constants of Ra-223 in RaF and Ra-223(+) are also calculated and compared with the experimental values wherever available to judge the extent of the accuracy obtained with the employed methods. The outcome of our study reveals that the Z-vector method is superior to the expectation-value approach in terms of accuracy obtained for the calculation of ground-state property. The Z-vector calculation shows that RaF has a high Eeff (52.5 GV/cm) and W-s (141.2 kHz), which makes it a potential candidate for the electric dipole moment of the electron (eEDM) experiment. An estimation of uncertainty associated with our final results is made, and it is found that it lies below 10\%.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.93.062506}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {42619, title = {Relativistic equation-of-motion coupled-cluster method for the electron attachment problem}, journal = {Computational and Theoretical Chemistry}, volume = {1076}, year = {2016}, month = {JAN}, pages = {94-100}, abstract = {

The article considers the successful implementation of relativistic equation-of-motion coupled cluster method for the electron attachment problem (EA-EOMCC) at the level of single- and double- excitation approximation. The implemented relativistic EA-EOMCC method is employed to calculate ionization potential values of alkali metal atoms (Li, Na, K, Rb, Cs, Fr) and the vertical electron affinity values of LiX (X = H, F, Cl, Br), NaY (Y = H, F, Cl) starting from their closed-shell configuration. Both four component and exact two-component calculations are done for all the opted systems. Further, we have shown the effect of spin-orbit interaction considering the atomic systems. The results of our atomic calculations are compared with the values from the NIST database and the results are found to be very accurate (\<1\%). (C) 2015 Elsevier B.V. All rights reserved.

}, doi = {10.1016/j.comptc.2015.12.015}, author = {Pathak, Himadri and Sasmal, Sudip and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {42621, title = {Search for parity and time reversal violating effects in HgH: relativistic coupled-cluster study}, journal = {Journal of Chemical Physics}, volume = {144}, year = {2016}, month = {MAR}, pages = {Article No. 124307}, abstract = {

The high effective electric field (E-eff) experienced by the unpaired electron in an atom or a molecule is one of the key ingredients in the success of electron electric dipole moment (eEDM) experiment and its precise calculation requires a very accurate theory. We, therefore, employed the Z-vector method in the relativistic coupled-cluster framework and found that HgH has a very large E-eff value (123.2 GV/cm) which makes it a potential candidate for the next generation eEDM experiment. Our study also reveals that it has a large scalar-pseudoscalar (S-PS) P, T-violating interaction constant, W-s = 284.2 kHz. To judge the accuracy of the obtained results, we have calculated parallel and perpendicular magnetic hyperfine structure (HFS) constants and compared with the available experimental values. The results of our calculation are found to be in nice agreement with the experimental values. Therefore, by looking at the HFS results, we can say that both E-eff and W-s values are also very accurate. Further, We have derived the relationship between these quantities and the ratio which will help to get model independent value of eEDM and S-PS interaction constant. (C) 2016 AIP Publishing LLC.

}, doi = {10.1063/1.4944673}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {44640, title = {Correlation trends in the magnetic hyperfine structure of atoms: a relativistic coupled-cluster case study}, journal = {Physical Review A}, volume = {98}, year = {2018}, month = {AUG}, type = {Article}, abstract = {

The role of electron correlation in the hyperfine structure of alkali metals and alkaline earth metal monopositive ions in their ground electronic configuration is investigated using the Z-vector method in a relativistic coupled-cluster regime within the singles and doubles approximation. The systematic effects of core-correlating functions, polarization of core electrons, and high-lying virtual functions on core electrons correlation are studied. The study reveals that the core-correlating function plays a significant role in core polarization and thus is very important for precise calculation of the wave function near the nuclear region. The inner-core electrons (1s-2p) require very high virtual energy functions for proper correlation. Therefore, the all-electron correlation treatment and the inclusion of higher-energy virtual functions are the key factors for precise calculation of the hyperfine structure constant of atoms. Our calculated values are in excellent agreement with the available experimental values, which also implies that the wave function produced by the Z-vector method is accurate enough for further calculation of the parity- and time-reversal symmetry-violating properties in atoms and molecules.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.98.022507}, author = {Talukdar, Kaushik and Sasmal, Sudip and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46172, title = {Nuclear parity- and time-reversal-symmetry violation in the (HgH)-Hg-201 molecule}, journal = {Physical Review A}, volume = {99}, year = {2019}, month = {MAR }, pages = {032503}, type = {Article}, abstract = {

Investigation of the nuclear magnetic quadrupole moment (MQM) is an excellent way to reveal the new physics in the hadron sector of matter. Therefore, we investigate the violation of parity (P) and time-reversal (T) invariance induced by the MQM of the( 201) Hg nucleus in the HgH molecule, which has been proposed as a very promising candidate for the experimental search of the electric dipole moment of electron [M. G. Kozlov and A. Derevianko, Phys. Rev. Lett. 97, 063001 (2006)]. We report the precise value of the molecular parameter, W-M, associated with the P, T-odd nuclear MQM-electron interaction in (HgH)-Hg-201 using the four-component relativistic coupled-cluster method. This parameter is required to interpret the experimental P, T-odd frequency shift in terms of the MQM of nuclei. Furthermore, the magnetic hyperfine structure (HFS) constants of the molecule are computed at the same level of theory. We also study the role of core-correlating functions and the virtual energy functions in the calculations of the HFS constant and W-M. The most reliable value of W(M )in HgH is obtained as 3.22 x 10 (33) Hz/e cm (2) with an uncertainty of around 6\%.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.032503}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46240, title = {Relativistic coupled-cluster investigation of parity (P) and time-reversal (T) symmetry violations in HgF}, journal = {Journal of Chemical Physics}, volume = {150}, year = {2019}, month = {FEB}, type = {Article}, abstract = {

We employ the Z-vector method in the four-component relativistic coupled-cluster framework to calculate the parity (P) and time-reversal (T) symmetry violating scalar-pseudoscalar nucleus-electron interaction constant (W-s), the effective electric field (E-eff) experienced by the unpaired electron, and the nuclear magnetic quadrupole moment-electron interaction constant (W-M) in the open-shell ground electronic state of HgF. The molecular frame dipole moment and the magnetic hyperfine structure (HFS) constant of the molecule are also calculated at the same level of theory. The outcome of our study is that HgF has a high value of E-eff (115.9 GV/cm), W-s (266.4 kHz), and W-M (3.59 x 10(33) Hz/e cm(2)), which shows that it can be a possible candidate for the search of new physics beyond the standard model. Our results are in good agreement with the available literature values. Furthermore, we investigate the effect of the basis set and the virtual energy functions on the computed properties. The role of the high-energy virtual spinors is found to be significant in the calculation of the HFS constant and the P,T-odd interaction coefficients. Published under license by AIP Publishing.

}, doi = {10.1063/1.5083000}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46641, title = {Electronic structure parameter of nuclear magnetic quadrupole moment interaction in metal monofluorides}, journal = {Journal of Chemical Physics}, volume = {153}, year = {2020}, month = {NOV}, pages = {184306}, type = {Article}, abstract = {

The electronic structure parameter (W-M) of the nuclear magnetic quadrupole moment (MQM) interaction in numerous open-shell metal monofluorides (viz., MgF, CaF, SrF, BaF, RaF, and PbF) is computed in the fully relativistic coupled-cluster framework. The electron-correlation effects are found to be very important for the precise calculation of W-M in the studied molecular systems. The molecular MQM interaction parameter scales nearly as Z(2) in the alkaline earth metal monofluorides, where Z is the nuclear charge of metal. Our study identifies (RaF)-Ra-223 as a good candidate for the experimental search of the nuclear MQM, which can help unravel the physics beyond the standard model in the hadron sector of matter.

}, issn = {0021-9606}, doi = {10.1063/5.0028669}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46788, title = {Relativistic coupled-cluster study of BaF in search of CP violation}, journal = {Journal of Physics B-Atomic Molecular and Optical Physics}, volume = {53}, year = {2020}, month = {JUL}, pages = {135102}, type = {Article}, abstract = {

BaF is one of the potential candidates for the experimental search of the electric dipole moment of the electron (eEDM). The NL-eEDM collaboration is building a new experimental set up to measure the eEDM using the BaF molecule (The NL-eEDM collaboration, 2018 Eur. Phys. J. D 72: 197). To analyze the results of such an experiment, one would require the accurate value of the molecular P, T-odd interaction parameters that cannot be measured from any experiment. In this work, we report the precise value of the P, T-odd interaction parameters of the BaF molecule obtained from the four-component relativistic coupled-cluster calculations. We also calculate the hyperfine structure (HFS) constants of the same molecule to assess the reliability of the reported molecular parameters. The calculated HFS constants show good agreement with the available experimental values. Further, the systematic effects of electron-correlation along with the roles of inner-core electrons and the virtual energy functions in the calculation of the studied properties of BaF are investigated.

}, keywords = {electric dipole moment of the electron, electron-correlation, Relativistic effects}, issn = {0953-4075}, doi = {10.1088/1361-6455/ab84c8}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46927, title = {Relativistic double-ionization equation-of-motion coupled-cluster method: application to low-lying doubly ionized states}, journal = {Journal of Chemical Physics}, volume = {152}, year = {2020}, month = {MAR}, pages = {104302}, type = {Article}, abstract = {

This article deals with the extension of the relativistic double-ionization equation-of-motion coupled-cluster (DI-EOMCC) method [H. Pathak et al. Phys. Rev. A 90, 010501(R) (2014)] for the molecular systems. The Dirac-Coulomb Hamiltonian with four-component spinors is considered to take care of the relativistic effects. The implemented method is employed to compute a few low-lying doubly ionized states of noble gas atoms (Ar, Kr, Xe, and Rn) and Cl-2, Br-2, HBr, and HI. Additionally, we presented results with two intermediate schemes in the four-component relativistic DI-EOMCC framework to understand the role of electron correlation. The computed double ionization spectra for the atomic systems are compared with the values from the non-relativistic DI-EOMCC method with spin-orbit coupling [Z. Wang et al. J. Chem. Phys. 142, 144109 (2015)] and the values from the National Institute of Science and Technology (NIST) database. Our atomic results are found to be in good agreement with the NIST values. Furthermore, the obtained results for the molecular systems agree well with the available experimental values.

}, issn = {0021-9606}, doi = {10.1063/1.5140988}, author = {Pathak, Himadri and Sasmal, Sudip and Talukdar, Kaushik and Nayak, Malaya K. and Veval, Nayana and Pal, Sourav} } @article {46932, title = {Role of electron correlation in the P, T-odd effects of CdH: a relativistic coupled-cluster investigation}, journal = {Physical Review A}, volume = {101}, year = {2020}, month = {MAR }, pages = {032505}, type = {Article}, abstract = {

We investigate the parity (P) and time-reversal (T) symmetry violating effects in the CdH molecule and perform the relativistic coupled-cluster calculation of the molecular parameters-E-eff, W-s, and W-M-related to the electric dipole moment of electron (eEDM) interaction, the scalar-pseudoscalar (S-PS) nucleus-electron neutral current coupling, and the nuclear magnetic quadrupole moment (MQM) interaction with electrons, respectively. We also compute the molecular dipole moment and the magnetic hyperfine structure coupling constant of CdH. The values of E-eff, W-s, and W-M obtained by us in the said molecule are 12.2 GV/cm, 14.0 kHz, and 0.82 x 10(33) Hz/e cm(2), respectively, within an uncertainty of 10\%. Furthermore, we study the trend of electron-correlation in the computed properties of CdH and that of the P, T-odd parameters in the group-12 monohydrides (i.e., ZnH, CdH, and HgH).

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.032505}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} }