M. Barbatti - Academia.edu (original) (raw)
Papers by M. Barbatti
Chemical Physics Letters, 2005
Semiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of... more Semiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of excited states of ethylene. Based on previous ab initio multireference configuration interaction results, a complete reparametrization of the AM1 semiempirical parameters was performed. Depending on the initial vertical excitation energy, lifetimes from 105 to 139 fs were found for the Vstate decay. Comparison to the pump-probe experiments was performed in order to explain the large differences between the theoretically and experimentally obtained lifetimes. The results show that probe energies of at least 7.4 eV should be employed to ionize the system for geometries close to the conical intersections.
Physical Chemistry Chemical Physics, 2010
The short-time photodynamics (2 ps) of formamide embedded into an Ar matrix starting from the low... more The short-time photodynamics (2 ps) of formamide embedded into an Ar matrix starting from the low-lying singlet excited S(1) (n(0)π*) and S(2) (ππ*) states were explored using a nonadiabatic photodynamics QM/MM approach. The interaction between formamide and the Ar matrix is taken into account at the MM level by means of Lennard-Jones potentials. This is the first example of exploring photodissociation of formamide with full nonadiabatic dynamics in a matrix and it nicely illustrates importance of considering environmental effects on photodissociation behavior of the peptide bond. It is shown that embedding of the formamide molecule in the argon matrix has strong impact on the outcome of the process. This is illustrated by formation of the 1:1 complex between ammonia and CO and prevention of full separation of the NH(2)˙ and HCO˙ subunits in the NH(2)˙ + HCO˙ radical pair. In addition, the argon matrix strongly influences the lifetime of the S(1) state, which increases by 211 fs relative to the gas phase.
Journal of Photochemistry and Photobiology A: Chemistry, 2007
The great importance of ultrafast phenomena in photochemistry and photobiology has made dynamics ... more The great importance of ultrafast phenomena in photochemistry and photobiology has made dynamics simulations an essential methodology in these areas. In this work, we present the Newton-X program package containing a new implementation of a direct dynamics approach to perform adiabatic (Born-Oppenheimer) and nonadiabatic simulations. The nonadiabatic dynamics is based on Tully's surface hopping approach. The program has been developed with the aim of (1) to create a flexible tool to be used in connection with a multitude of third-party electronicstructure program packages and (2) to provide the most common options for excited-state dynamics simulations. Benchmark calculations on the nonadiabatic dynamics are presented for the methaniminium, butatriene and pentadieniminium cations. The simulation of UV absorption spectra is presented for the methaniminium cation and pyrazine.
Journal of Chemical Theory and Computation, 2013
Donor−acceptor heterojunctions composed of thiophene oligomers and C 60 fullerene were investigat... more Donor−acceptor heterojunctions composed of thiophene oligomers and C 60 fullerene were investigated with computational methods. Benchmark calculations were performed with time-dependent density functional theory. The effects of varying the density functional, the number of oligomers, the intermolecular distance, the medium polarization, and the chemical functionalization of the monomers were analyzed. The results are presented in terms of diagrams where the electronic states are classified as locally excited states, charge-transfer states, and delocalized states. The effects of each option for computational simulations of realistic heterojunctions employed in photovoltaic devices are evaluated and discussed.
The Journal of Chemical Physics, 2006
Multireference configuration interaction ͑MRCI͒ calculations have been performed for pyrrole with... more Multireference configuration interaction ͑MRCI͒ calculations have been performed for pyrrole with the aim of providing an explanation for the experimentally observed photochemical deactivation processes. Potential energy curves and minima on the crossing seam were determined using the analytic MRCI gradient and nonadiabatic coupling features of the COLUMBUS program system. A new deactivation mechanism based on an out-of-plane ring deformation is presented. This mechanism directly couples the charge transfer 1 * and ground states. It may be responsible for more than 50% of the observed photofragments of * -excited pyrrole. The ring deformation mechanism should act complementary to the previously proposed NH-stretching mechanism, thus offering a more complete interpretation of the pyrrole photodynamics.
The Journal of Chemical Physics, 2006
The problem of the double bond flipping interconversion of the two equivalent ground state struct... more The problem of the double bond flipping interconversion of the two equivalent ground state structures of cyclobutadiene ͑CBD͒ is addressed at the multireference average-quadratic coupled cluster level of theory, which is capable of optimizing the structural parameters of the ground, transition, and excited states on an equal footing. The barrier height involving both the electronic and zero-point vibrational energy contributions is 6.3 kcal mol −1 , which is higher than the best earlier theoretical estimate of 4.0 kcal mol −1 . This result is confirmed by including into the reference space the orbitals of the CC bonds beyond the standard orbital space. It places the present value into the middle of the range of the measured data ͑1.6-10 kcal mol −1 ͒. An adiabatic singlet-triplet energy gap of 7.4 kcal mol −1 between the transition state 1 B tg and the first triplet 3 A 2g state is obtained. A low barrier height for the CBD automerization and a small ⌬E͑ 3 A 2g , 1 B 1g ͒ gap bear some relevance on the highly pronounced reactivity of CBD, which is briefly discussed.
![Research paper thumbnail of The structure and the thermochemical properties of the H[sub 3][sup +](H[sub 2])[sub n] clusters (n=8–12)](https://attachments.academia-assets.com/44150186/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2001
Ab initio calculations were performed for the H 3 ϩ ͑H 2 ) n clusters (nϭ8 -12), including comple... more Ab initio calculations were performed for the H 3 ϩ ͑H 2 ) n clusters (nϭ8 -12), including complete optimization of several isomers of the nϭ10 cluster. Binding energies, enthalpies, and ionization potentials are calculated. Well defined patterns of chromism are predicted for the H 2 collective vibrations and for the H 3 ϩ breathing vibrations. The calculations for the nϾ10 clusters allow us to understand their shell structure in terms of concentric spheres of H 2 molecules. The first and second shells have occupation numbers equal to 3 and 6, respectively, while for the third shell, this number is within the range 12-15.
Chemical Physics, 2008
We investigate the non-radiative decay in the photo-isomerization of the dideuterated methanimini... more We investigate the non-radiative decay in the photo-isomerization of the dideuterated methaniminium cation HDN+CDH by means of quantum dynamical simulations of the laser driven torsion. For the present model, the torsional dynamics is nearly adiabatic, but this is shown to be extremely sensitive to the large non-adiabatic coupling elements close to the conical intersection as well as to the apparently
Chemical Physics Letters, 2005
Semiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of... more Semiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of excited states of ethylene. Based on previous ab initio multireference configuration interaction results, a complete reparametrization of the AM1 semiempirical parameters was performed. Depending on the initial vertical excitation energy, lifetimes from 105 to 139 fs were found for the Vstate decay. Comparison to the pump-probe experiments was performed in order to explain the large differences between the theoretically and experimentally obtained lifetimes. The results show that probe energies of at least 7.4 eV should be employed to ionize the system for geometries close to the conical intersections.
Chemical Physics Letters, 2005
Semiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of... more Semiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of excited states of ethylene. Based on previous ab initio multireference configuration interaction results, a complete reparametrization of the AM1 semiempirical parameters was performed. Depending on the initial vertical excitation energy, lifetimes from 105 to 139 fs were found for the Vstate decay. Comparison to the pump-probe experiments was performed in order to explain the large differences between the theoretically and experimentally obtained lifetimes. The results show that probe energies of at least 7.4 eV should be employed to ionize the system for geometries close to the conical intersections.
Physical Chemistry Chemical Physics, 2010
The short-time photodynamics (2 ps) of formamide embedded into an Ar matrix starting from the low... more The short-time photodynamics (2 ps) of formamide embedded into an Ar matrix starting from the low-lying singlet excited S(1) (n(0)π*) and S(2) (ππ*) states were explored using a nonadiabatic photodynamics QM/MM approach. The interaction between formamide and the Ar matrix is taken into account at the MM level by means of Lennard-Jones potentials. This is the first example of exploring photodissociation of formamide with full nonadiabatic dynamics in a matrix and it nicely illustrates importance of considering environmental effects on photodissociation behavior of the peptide bond. It is shown that embedding of the formamide molecule in the argon matrix has strong impact on the outcome of the process. This is illustrated by formation of the 1:1 complex between ammonia and CO and prevention of full separation of the NH(2)˙ and HCO˙ subunits in the NH(2)˙ + HCO˙ radical pair. In addition, the argon matrix strongly influences the lifetime of the S(1) state, which increases by 211 fs relative to the gas phase.
Journal of Photochemistry and Photobiology A: Chemistry, 2007
The great importance of ultrafast phenomena in photochemistry and photobiology has made dynamics ... more The great importance of ultrafast phenomena in photochemistry and photobiology has made dynamics simulations an essential methodology in these areas. In this work, we present the Newton-X program package containing a new implementation of a direct dynamics approach to perform adiabatic (Born-Oppenheimer) and nonadiabatic simulations. The nonadiabatic dynamics is based on Tully's surface hopping approach. The program has been developed with the aim of (1) to create a flexible tool to be used in connection with a multitude of third-party electronicstructure program packages and (2) to provide the most common options for excited-state dynamics simulations. Benchmark calculations on the nonadiabatic dynamics are presented for the methaniminium, butatriene and pentadieniminium cations. The simulation of UV absorption spectra is presented for the methaniminium cation and pyrazine.
Journal of Chemical Theory and Computation, 2013
Donor−acceptor heterojunctions composed of thiophene oligomers and C 60 fullerene were investigat... more Donor−acceptor heterojunctions composed of thiophene oligomers and C 60 fullerene were investigated with computational methods. Benchmark calculations were performed with time-dependent density functional theory. The effects of varying the density functional, the number of oligomers, the intermolecular distance, the medium polarization, and the chemical functionalization of the monomers were analyzed. The results are presented in terms of diagrams where the electronic states are classified as locally excited states, charge-transfer states, and delocalized states. The effects of each option for computational simulations of realistic heterojunctions employed in photovoltaic devices are evaluated and discussed.
The Journal of Chemical Physics, 2006
Multireference configuration interaction ͑MRCI͒ calculations have been performed for pyrrole with... more Multireference configuration interaction ͑MRCI͒ calculations have been performed for pyrrole with the aim of providing an explanation for the experimentally observed photochemical deactivation processes. Potential energy curves and minima on the crossing seam were determined using the analytic MRCI gradient and nonadiabatic coupling features of the COLUMBUS program system. A new deactivation mechanism based on an out-of-plane ring deformation is presented. This mechanism directly couples the charge transfer 1 * and ground states. It may be responsible for more than 50% of the observed photofragments of * -excited pyrrole. The ring deformation mechanism should act complementary to the previously proposed NH-stretching mechanism, thus offering a more complete interpretation of the pyrrole photodynamics.
The Journal of Chemical Physics, 2006
The problem of the double bond flipping interconversion of the two equivalent ground state struct... more The problem of the double bond flipping interconversion of the two equivalent ground state structures of cyclobutadiene ͑CBD͒ is addressed at the multireference average-quadratic coupled cluster level of theory, which is capable of optimizing the structural parameters of the ground, transition, and excited states on an equal footing. The barrier height involving both the electronic and zero-point vibrational energy contributions is 6.3 kcal mol −1 , which is higher than the best earlier theoretical estimate of 4.0 kcal mol −1 . This result is confirmed by including into the reference space the orbitals of the CC bonds beyond the standard orbital space. It places the present value into the middle of the range of the measured data ͑1.6-10 kcal mol −1 ͒. An adiabatic singlet-triplet energy gap of 7.4 kcal mol −1 between the transition state 1 B tg and the first triplet 3 A 2g state is obtained. A low barrier height for the CBD automerization and a small ⌬E͑ 3 A 2g , 1 B 1g ͒ gap bear some relevance on the highly pronounced reactivity of CBD, which is briefly discussed.
The Journal of Chemical Physics, 2001
Ab initio calculations were performed for the H 3 ϩ ͑H 2 ) n clusters (nϭ8 -12), including comple... more Ab initio calculations were performed for the H 3 ϩ ͑H 2 ) n clusters (nϭ8 -12), including complete optimization of several isomers of the nϭ10 cluster. Binding energies, enthalpies, and ionization potentials are calculated. Well defined patterns of chromism are predicted for the H 2 collective vibrations and for the H 3 ϩ breathing vibrations. The calculations for the nϾ10 clusters allow us to understand their shell structure in terms of concentric spheres of H 2 molecules. The first and second shells have occupation numbers equal to 3 and 6, respectively, while for the third shell, this number is within the range 12-15.
Chemical Physics, 2008
We investigate the non-radiative decay in the photo-isomerization of the dideuterated methanimini... more We investigate the non-radiative decay in the photo-isomerization of the dideuterated methaniminium cation HDN+CDH by means of quantum dynamical simulations of the laser driven torsion. For the present model, the torsional dynamics is nearly adiabatic, but this is shown to be extremely sensitive to the large non-adiabatic coupling elements close to the conical intersection as well as to the apparently
Chemical Physics Letters, 2005
Semiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of... more Semiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of excited states of ethylene. Based on previous ab initio multireference configuration interaction results, a complete reparametrization of the AM1 semiempirical parameters was performed. Depending on the initial vertical excitation energy, lifetimes from 105 to 139 fs were found for the Vstate decay. Comparison to the pump-probe experiments was performed in order to explain the large differences between the theoretically and experimentally obtained lifetimes. The results show that probe energies of at least 7.4 eV should be employed to ionize the system for geometries close to the conical intersections.