Abstract The Born–Oppenheimer (BO) approximation is the bedrock of quantum mechanical calculation... more Abstract The Born–Oppenheimer (BO) approximation is the bedrock of quantum mechanical calculations of atomic and molecular systems. However, there are effects in these systems that require departure from the BO approximations. We start this review with describing these effects and some of the previous works where calculations were performed to account for their magnitude in various atomic and molecular properties. In particular, the problem of selecting appropriate basis functions for non-BO calculations is analyzed and some examples of such calculations are presented. The last part of this review is devoted to perspectives in carrying out quantum mechanical studies of structures, spectra, and other properties of atoms and molecules in isolation and in confinement and treating both nuclei and electrons in these studies on on equal footing.
Highly accurate calculations are reported for the eleven lowest states of the 2 P Rydberg series ... more Highly accurate calculations are reported for the eleven lowest states of the 2 P Rydberg series (1s 2 np 1, n = 2, …, 12) of the lithium atom. The nonrelativistic wave functions of the states are expanded in terms of up to 16 000 all-electron explicitly correlated Gaussian (ECG) basis functions. The ECG exponential parameters are variationally optimized using a method that employs the analytical energy gradient determined for the parameters. The finite-nuclear-mass effects of the 6Li and 7Li isotopes are explicitly included in the nonrelativistic variational calculations. The results also include the leading relativistic and quantum electrodynamics energy corrections computed using the framework of perturbation theory. The calculated interstate transition energies are compared with the available experimental data. The 6Li–7Li isotope shifts of the transition energies are determined.
Journal of Physics B: Atomic, Molecular and Optical Physics
Highly accurate calculations are reported for the eleven lowest states of the 2 P Rydberg series ... more Highly accurate calculations are reported for the eleven lowest states of the 2 P Rydberg series (1s 2 np 1, n = 2, …, 12) of the lithium atom. The nonrelativistic wave functions of the states are expanded in terms of up to 16 000 all-electron explicitly correlated Gaussian (ECG) basis functions. The ECG exponential parameters are variationally optimized using a method that employs the analytical energy gradient determined for the parameters. The finite-nuclear-mass effects of the 6Li and 7Li isotopes are explicitly included in the nonrelativistic variational calculations. The results also include the leading relativistic and quantum electrodynamics energy corrections computed using the framework of perturbation theory. The calculated interstate transition energies are compared with the available experimental data. The 6Li–7Li isotope shifts of the transition energies are determined.
Abstract The Born–Oppenheimer (BO) approximation is the bedrock of quantum mechanical calculation... more Abstract The Born–Oppenheimer (BO) approximation is the bedrock of quantum mechanical calculations of atomic and molecular systems. However, there are effects in these systems that require departure from the BO approximations. We start this review with describing these effects and some of the previous works where calculations were performed to account for their magnitude in various atomic and molecular properties. In particular, the problem of selecting appropriate basis functions for non-BO calculations is analyzed and some examples of such calculations are presented. The last part of this review is devoted to perspectives in carrying out quantum mechanical studies of structures, spectra, and other properties of atoms and molecules in isolation and in confinement and treating both nuclei and electrons in these studies on on equal footing.
All‐electron fixed‐node diffusion quantum Monte Carlo energies of the two lowest‐lying states of ... more All‐electron fixed‐node diffusion quantum Monte Carlo energies of the two lowest‐lying states of C, N, O, F, and Ne atoms are reported. The Slater‐Jastrow form is used as the trial wave function. We will use single‐ and multideterminant wave functions as the Slater part. The single‐determinant wave function has been computed by the Hartree‐Fock method and the multideterminant wave functions have been computed by the complete active space self‐consistent field, configuration interaction with single and double excitation, configuration interaction with single, double, triple, and quadruple excitation and second‐order configuration interaction. For the ground‐ and first excited states, the multideterminant wave functions have computed more than 99% of the correlation energy. Significant improvements have been achieved using the backflow transformations and up to 99.8% of the correlation energy has been recovered. A very good agreement with the experimental data has been obtained for th...
Complete phase diagrams for the poly ethylene glycol di-methyl ether 2000 (PEGDME 2000 )+Na 3 PO ... more Complete phase diagrams for the poly ethylene glycol di-methyl ether 2000 (PEGDME 2000 )+Na 3 PO 4 +H 2 O system at T = (298.15, 308.15 and 318.15) K were determined. Liquidliquid equilibria (LLE) for the aqueous PEGDME 2000 +Na 3 PO 4 system were determined ...
Abstract The Born–Oppenheimer (BO) approximation is the bedrock of quantum mechanical calculation... more Abstract The Born–Oppenheimer (BO) approximation is the bedrock of quantum mechanical calculations of atomic and molecular systems. However, there are effects in these systems that require departure from the BO approximations. We start this review with describing these effects and some of the previous works where calculations were performed to account for their magnitude in various atomic and molecular properties. In particular, the problem of selecting appropriate basis functions for non-BO calculations is analyzed and some examples of such calculations are presented. The last part of this review is devoted to perspectives in carrying out quantum mechanical studies of structures, spectra, and other properties of atoms and molecules in isolation and in confinement and treating both nuclei and electrons in these studies on on equal footing.
Highly accurate calculations are reported for the eleven lowest states of the 2 P Rydberg series ... more Highly accurate calculations are reported for the eleven lowest states of the 2 P Rydberg series (1s 2 np 1, n = 2, …, 12) of the lithium atom. The nonrelativistic wave functions of the states are expanded in terms of up to 16 000 all-electron explicitly correlated Gaussian (ECG) basis functions. The ECG exponential parameters are variationally optimized using a method that employs the analytical energy gradient determined for the parameters. The finite-nuclear-mass effects of the 6Li and 7Li isotopes are explicitly included in the nonrelativistic variational calculations. The results also include the leading relativistic and quantum electrodynamics energy corrections computed using the framework of perturbation theory. The calculated interstate transition energies are compared with the available experimental data. The 6Li–7Li isotope shifts of the transition energies are determined.
Journal of Physics B: Atomic, Molecular and Optical Physics
Highly accurate calculations are reported for the eleven lowest states of the 2 P Rydberg series ... more Highly accurate calculations are reported for the eleven lowest states of the 2 P Rydberg series (1s 2 np 1, n = 2, …, 12) of the lithium atom. The nonrelativistic wave functions of the states are expanded in terms of up to 16 000 all-electron explicitly correlated Gaussian (ECG) basis functions. The ECG exponential parameters are variationally optimized using a method that employs the analytical energy gradient determined for the parameters. The finite-nuclear-mass effects of the 6Li and 7Li isotopes are explicitly included in the nonrelativistic variational calculations. The results also include the leading relativistic and quantum electrodynamics energy corrections computed using the framework of perturbation theory. The calculated interstate transition energies are compared with the available experimental data. The 6Li–7Li isotope shifts of the transition energies are determined.
Abstract The Born–Oppenheimer (BO) approximation is the bedrock of quantum mechanical calculation... more Abstract The Born–Oppenheimer (BO) approximation is the bedrock of quantum mechanical calculations of atomic and molecular systems. However, there are effects in these systems that require departure from the BO approximations. We start this review with describing these effects and some of the previous works where calculations were performed to account for their magnitude in various atomic and molecular properties. In particular, the problem of selecting appropriate basis functions for non-BO calculations is analyzed and some examples of such calculations are presented. The last part of this review is devoted to perspectives in carrying out quantum mechanical studies of structures, spectra, and other properties of atoms and molecules in isolation and in confinement and treating both nuclei and electrons in these studies on on equal footing.
All‐electron fixed‐node diffusion quantum Monte Carlo energies of the two lowest‐lying states of ... more All‐electron fixed‐node diffusion quantum Monte Carlo energies of the two lowest‐lying states of C, N, O, F, and Ne atoms are reported. The Slater‐Jastrow form is used as the trial wave function. We will use single‐ and multideterminant wave functions as the Slater part. The single‐determinant wave function has been computed by the Hartree‐Fock method and the multideterminant wave functions have been computed by the complete active space self‐consistent field, configuration interaction with single and double excitation, configuration interaction with single, double, triple, and quadruple excitation and second‐order configuration interaction. For the ground‐ and first excited states, the multideterminant wave functions have computed more than 99% of the correlation energy. Significant improvements have been achieved using the backflow transformations and up to 99.8% of the correlation energy has been recovered. A very good agreement with the experimental data has been obtained for th...
Complete phase diagrams for the poly ethylene glycol di-methyl ether 2000 (PEGDME 2000 )+Na 3 PO ... more Complete phase diagrams for the poly ethylene glycol di-methyl ether 2000 (PEGDME 2000 )+Na 3 PO 4 +H 2 O system at T = (298.15, 308.15 and 318.15) K were determined. Liquidliquid equilibria (LLE) for the aqueous PEGDME 2000 +Na 3 PO 4 system were determined ...
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Papers by Saeed Nasiri