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Bernhard H Schlegel - One of the best experts on this subject based on the ideXlab platform.
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angular dependence of strong field ionization of n2 by time dependent configuration interaction using density functional theory and the tamm dancoff approximation
Journal of Chemical Physics, 2019Co-Authors: Paul Hoerner, Mi Kyung Lee, Bernhard H SchlegelAbstract:The ionization of N2 serves as an important test case for computational methods for strong field ionization. Because Koopmans’s theorem fails for Hartree-Fock calculations of N2, corrections for electron correlation are needed to obtain the proper ordering of ionization energies of N2. Lopata and co-workers found that real-time integration of time-dependent Hartree-Fock (rt-TD-HF) gave a ratio for strong field ionization parallel and perpendicular to the Molecular Axis that was too small compared to experiment, but real-time integration of time-dependent density functional theory (rt-TD-DFT) with an appropriately tuned long-range corrected functional, lc-ωPBE*, was in good agreement with experiment. The present study finds that time-dependent configuration interaction (TDCI) with single excitations based on a Hartree-Fock reference determinant (TD-CIS) has the same problems as rt-TD-HF. These problems can be overcome within the TDCI framework by calculating the excitation energies and transition dipole moments with density functional theory using linear response TD-DFT in the Tamm-Dancoff approximation (TDA) with suitably tuned long-range corrected functionals (TD-TDA). The correct angular dependence of the total ionization rate is obtained with TD-TDA using tuned lc-ωPBE*, lc-BLYP*, and ωB97XD* functionals. Partitioning of the total ionization rate into orbital components confirms that the larger ionization rate perpendicular to the Molecular Axis found for TD-CIS is due to greater π orbital contributions than those seen in TD-TDA. The use of density functional theory corrects this problem. At higher fields, both the TD-CIS and TD-TDA simulations show an increased ionization rate perpendicular to the Molecular Axis because of increased ionization from the π orbitals.The ionization of N2 serves as an important test case for computational methods for strong field ionization. Because Koopmans’s theorem fails for Hartree-Fock calculations of N2, corrections for electron correlation are needed to obtain the proper ordering of ionization energies of N2. Lopata and co-workers found that real-time integration of time-dependent Hartree-Fock (rt-TD-HF) gave a ratio for strong field ionization parallel and perpendicular to the Molecular Axis that was too small compared to experiment, but real-time integration of time-dependent density functional theory (rt-TD-DFT) with an appropriately tuned long-range corrected functional, lc-ωPBE*, was in good agreement with experiment. The present study finds that time-dependent configuration interaction (TDCI) with single excitations based on a Hartree-Fock reference determinant (TD-CIS) has the same problems as rt-TD-HF. These pr...
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angular dependence of strong field ionization of haloacetylenes hccx x f cl br i using time dependent configuration interaction with an absorbing potential
Journal of Physical Chemistry C, 2018Co-Authors: Paul Hoerner, Bernhard H SchlegelAbstract:Strong field ionization of haloacetylenes was simulated by time-dependent configuration interaction using all single excitations and a complex absorbing potential. The angular dependence of ionization for HCCX was mapped with static electric fields in the range 0.01–0.06 atomic units and compared with the results for CH3X. HCCF ionizes primarily from the CC π orbital. HCCX (X = Cl, Br, I) compounds show increasing amounts of ionization from the halogen π-type lone pair orbitals and have a node perpendicular to the Molecular Axis. These shapes can be understood in terms of the energies and interactions of the halogen π-type lone pairs with the π orbitals of the CC triple bond.
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strong field ionization rates of linear polyenes simulated with time dependent configuration interaction with an absorbing potential
Journal of Chemical Physics, 2014Co-Authors: Pascal Krause, Bernhard H SchlegelAbstract:The strong field ionization rates for ethylene, trans 1,3-butadiene, and trans,trans 1,3,5-hexatriene have been calculated using time-dependent configuration interaction with single excitations and a complex absorbing potential (TDCIS-CAP). The calculations used the aug-cc-pVTZ basis set with a large set of diffuse functions (3 s, 2 p, 3 d, and 1 f) on each atom. The absorbing boundary was placed 3.5 times the van der Waals radius from each atom. The simulations employed a seven-cycle cosine squared pulse with a wavelength of 800 nm. Ionization rates were calculated for intensities ranging from 0.3 × 1014 W/cm2 to 3.5 × 1014 W/cm2. Ionization rates along the Molecular Axis increased markedly with increasing conjugation length. By contrast, ionization rates perpendicular to the Molecular Axis were almost independent of the conjugation length.
P B Corkum - One of the best experts on this subject based on the ideXlab platform.
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alignment dependent enhancement of the photoelectron cutoff for multiphoton ionization of molecules
Physical Review Letters, 2014Co-Authors: C. Smeenk, Ladan Arissian, Alexei V Sokolov, Michael Spanner, Kurnchul Lee, A Staudte, D M Villeneuve, P B CorkumAbstract:The multiphoton ionization rate of molecules depends on the alignment of the Molecular Axis with respect to the ionizing laser polarization. By studying Molecular frame photoelectron angular distributions from ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, and benzene, we illustrate how the angle-dependent ionization rate affects the photoelectron cutoff energy. We find alignment can enhance the high energy cutoff of the photoelectron spectrum when probing along a nodal plane or when ionization is otherwise suppressed. This is supported by calculations using a tunneling model with a single ion state.
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Molecular reorientation during dissociative multiphoton ionization
Physical Review A, 1993Co-Authors: P Dietrich, D Strickland, Michel Laberge, P B CorkumAbstract:The angular distribution of the ion fragments after multiphoton ionization of diatomic molecules shows a pronounced anisotropy. Fragments are detected mainly along the direction of the laser polarization, as is shown for iodine in this paper. We have performed a double-pulse experiment to clarify the underlying mechanism. It shows that the anisotropy cannot be explained in terms of a variation of the ionization rates with the angle between the electric field and the Molecular Axis. Instead, the anisotropy is caused by the deflection of the ion fragments in the strong field due to the Molecular polarizability. Although the molecules are frozen in space on the time scale of the laser pulse, they gain enough angular momentum to affect the trajectories of the fragments. Classical trajectory calculations support this explanation.
Abraham H Parola - One of the best experts on this subject based on the ideXlab platform.
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a structural view of the dissociation of escherichia coli tryptophanase
Biophysical Journal, 2017Co-Authors: Abraham H Parola, Keren Green, Nasrin Qasem, Garik Y Gdalevsky, Anna Kogan, Yehuda Goldgur, Ofra Lotan, Orna AlmogAbstract:Tryptophanase (Trpase) is a pyridoxal 5′-phosphate (PLP)-dependent homotetrameric enzyme which catalyzes the degradation of l-tryptophan. Trpase is known for its cold lability, i.e., a reversible loss of activity at low temperature (2°C), associated with tetramer dissociation. Escherichia coli Trpase dissociates into dimers, while Proteus vulgaris Trpase dissociates into monomers. Accordingly, Trpase is an appropriate model to study the quaternary structure of proteins. We aimed at understanding the differences in the mode of dissociation between the E. coli and P. vulgaris Trpases. In particular, the effect of mutations along the Molecular axes of homotetrameric Trpase on its dissociation was studied. Two groups of mutants of the E. coli enzyme were created to resemble the amino-acid sequence of P. vulgaris Trpase. In one, residues 15 and 59 that are located along the Molecular Axis R (termed the noncatalytic Axis) were mutated. The second group included a mutation at position 298, located along the Molecular Axis Q (termed the catalytic Axis). Replacing amino-acid residues along the R Axis resulted in dissociation of the tetramers into monomers, similar to the P. vulgaris Trpase, while replacing amino-acid residues along the Q Axis resulted in dissociation into dimers only. The crystal structure of the V59M mutant of E. coli Trpase was also determined in its apo form and was found to be similar to that of the wild type. This study suggests that in E. coli Trpase hydrophobic interactions along the R Axis hold the two monomers together more strongly, preventing the dissociation of the dimers into monomers. Mutation of position 298 along the Q Axis to a charged residue resulted in tetramers that are less susceptible to dissociation. The results indicate that dissociation of E. coli Trpase into dimers occurs along the Molecular Q Axis.
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a structural view of the dissociation of escherichia coli tryptophanase
Acta Crystallographica Section D-biological Crystallography, 2015Co-Authors: Keren Green, Abraham H Parola, Anna Kogan, Yehuda Goldgur, Ofra Lotan, Nasrin Qasim, Garik Gdaelvsky, Orna AlmogAbstract:: Tryptophanase (Trpase) is a pyridoxal 5'-phosphate (PLP)-dependent homotetrameric enzyme which catalyzes the degradation of L-tryptophan. Trpase is also known for its cold lability, which is a reversible loss of activity at low temperature (2°C) that is associated with the dissociation of the tetramer. Escherichia coli Trpase dissociates into dimers, while Proteus vulgaris Trpase dissociates into monomers. As such, this enzyme is an appropriate model to study the protein-protein interactions and quaternary structure of proteins. The aim of the present study was to understand the differences in the mode of dissociation between the E. coli and P. vulgaris Trpases. In particular, the effect of mutations along the Molecular axes of homotetrameric Trpase on its dissociation was studied. To answer this question, two groups of mutants of the E. coli enzyme were created to resemble the amino-acid sequence of P. vulgaris Trpase. In one group, residues 15 and 59 that are located along the Molecular Axis R (also termed the noncatalytic Axis) were mutated. The second group included a mutation at position 298, located along the Molecular Axis Q (also termed the catalytic Axis). Replacing amino-acid residues along the R Axis resulted in dissociation of the tetramers into monomers, similar to the P. vulgaris Trpase, while replacing amino-acid residues along the Q Axis resulted in dissociation into dimers only. The crystal structure of the V59M mutant of E. coli Trpase was also determined in its apo form and was found to be similar to that of the wild type. This study suggests that in E. coli Trpase hydrophobic interactions along the R Axis hold the two monomers together more strongly, preventing the dissociation of the dimers into monomers. Mutation of position 298 along the Q Axis to a charged residue resulted in tetramers that are less susceptible to dissociation. Thus, the results indicate that dissociation of E. coli Trpase into dimers occurs along the Molecular Q Axis.
Orna Almog - One of the best experts on this subject based on the ideXlab platform.
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a structural view of the dissociation of escherichia coli tryptophanase
Biophysical Journal, 2017Co-Authors: Abraham H Parola, Keren Green, Nasrin Qasem, Garik Y Gdalevsky, Anna Kogan, Yehuda Goldgur, Ofra Lotan, Orna AlmogAbstract:Tryptophanase (Trpase) is a pyridoxal 5′-phosphate (PLP)-dependent homotetrameric enzyme which catalyzes the degradation of l-tryptophan. Trpase is known for its cold lability, i.e., a reversible loss of activity at low temperature (2°C), associated with tetramer dissociation. Escherichia coli Trpase dissociates into dimers, while Proteus vulgaris Trpase dissociates into monomers. Accordingly, Trpase is an appropriate model to study the quaternary structure of proteins. We aimed at understanding the differences in the mode of dissociation between the E. coli and P. vulgaris Trpases. In particular, the effect of mutations along the Molecular axes of homotetrameric Trpase on its dissociation was studied. Two groups of mutants of the E. coli enzyme were created to resemble the amino-acid sequence of P. vulgaris Trpase. In one, residues 15 and 59 that are located along the Molecular Axis R (termed the noncatalytic Axis) were mutated. The second group included a mutation at position 298, located along the Molecular Axis Q (termed the catalytic Axis). Replacing amino-acid residues along the R Axis resulted in dissociation of the tetramers into monomers, similar to the P. vulgaris Trpase, while replacing amino-acid residues along the Q Axis resulted in dissociation into dimers only. The crystal structure of the V59M mutant of E. coli Trpase was also determined in its apo form and was found to be similar to that of the wild type. This study suggests that in E. coli Trpase hydrophobic interactions along the R Axis hold the two monomers together more strongly, preventing the dissociation of the dimers into monomers. Mutation of position 298 along the Q Axis to a charged residue resulted in tetramers that are less susceptible to dissociation. The results indicate that dissociation of E. coli Trpase into dimers occurs along the Molecular Q Axis.
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a structural view of the dissociation of escherichia coli tryptophanase
Acta Crystallographica Section D-biological Crystallography, 2015Co-Authors: Keren Green, Abraham H Parola, Anna Kogan, Yehuda Goldgur, Ofra Lotan, Nasrin Qasim, Garik Gdaelvsky, Orna AlmogAbstract:: Tryptophanase (Trpase) is a pyridoxal 5'-phosphate (PLP)-dependent homotetrameric enzyme which catalyzes the degradation of L-tryptophan. Trpase is also known for its cold lability, which is a reversible loss of activity at low temperature (2°C) that is associated with the dissociation of the tetramer. Escherichia coli Trpase dissociates into dimers, while Proteus vulgaris Trpase dissociates into monomers. As such, this enzyme is an appropriate model to study the protein-protein interactions and quaternary structure of proteins. The aim of the present study was to understand the differences in the mode of dissociation between the E. coli and P. vulgaris Trpases. In particular, the effect of mutations along the Molecular axes of homotetrameric Trpase on its dissociation was studied. To answer this question, two groups of mutants of the E. coli enzyme were created to resemble the amino-acid sequence of P. vulgaris Trpase. In one group, residues 15 and 59 that are located along the Molecular Axis R (also termed the noncatalytic Axis) were mutated. The second group included a mutation at position 298, located along the Molecular Axis Q (also termed the catalytic Axis). Replacing amino-acid residues along the R Axis resulted in dissociation of the tetramers into monomers, similar to the P. vulgaris Trpase, while replacing amino-acid residues along the Q Axis resulted in dissociation into dimers only. The crystal structure of the V59M mutant of E. coli Trpase was also determined in its apo form and was found to be similar to that of the wild type. This study suggests that in E. coli Trpase hydrophobic interactions along the R Axis hold the two monomers together more strongly, preventing the dissociation of the dimers into monomers. Mutation of position 298 along the Q Axis to a charged residue resulted in tetramers that are less susceptible to dissociation. Thus, the results indicate that dissociation of E. coli Trpase into dimers occurs along the Molecular Q Axis.
Dmitry A Telnov - One of the best experts on this subject based on the ideXlab platform.
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effects of multiple electronic shells on strong field multiphoton ionization and high order harmonic generation of diatomic molecules with arbitrary orientation an all electron time dependent density functional approach
Physical Review A, 2009Co-Authors: Dmitry A Telnov, Shihi ChuAbstract:We present a time-dependent density-functional theory approach with proper long-range potential for an ab initio study of the effect of correlated multielectron responses on the multiphoton ionization (MPI) and high-order harmonic generation (HHG) of diatomic molecules ${\text{N}}_{2}$ and ${\text{F}}_{2}$ in intense short laser pulse fields with arbitrary Molecular orientation. We show that the contributions of inner Molecular orbitals to the total MPI probability can be sufficiently large or even dominant over the highest-occupied Molecular orbital, depending on detailed electronic structure and symmetry, laser field intensity, and orientation angle. The multielectron effects in HHG are also very important. They are responsible for enhanced HHG at some orientations of the Molecular Axis. Even strongly bound electrons may have a significant influence on the HHG process.