TY - JOUR

T1 - Structure and spectrum of the hydrated electron. A combined quantum chemical statistical mechanical simulation

AU - Hermida-Ramon, Jose M.

AU - Öhrn, Anders

AU - Karlström, Gunnar

PY - 2019

Y1 - 2019

N2 - In the current work, in order to model a free electron solvated in water, we have implemented a method to represent the molecular charge distribution as a set of Slater-type functions within the framework of a QM/MM method called QMSTAT. Also, it has been introduced in this method a new approach to calculate the intermolecular induction energy in the presence of very strong electric fields. Unlike most previous potentials, our method uses the ab initio energies of the electron-water complex as reference to obtain the few fitted parameters that the model needs, instead of the ab initio potential of the electron. A Metropolis-Monte Carlo simulation of 15 million steps has been carried out in a system that consists of an electron solvated in 200 water molecules explicitly described. The obtained results predict a vertical electron detachment energy of 3.30 eV and a radius of gyration of 2.38 Å, which are in very good agreement with the experimental data of 3.27 ± 0.10 eV and 2.45 Å, respectively. We have also obtained the absorption spectrum of the hydrated electron from our simulation. The maximum of the spectrum agrees very well with the experimental result and the experimental width at half-maximum is only 0.11 eV wider than the calculated curve. The calculations predict the same blue tail as the experimental result but with a less smooth shape. Also, our results indicate that the transfer of intensity from the transition arriving to the highest of the three p states to transitions arriving to higher-lying states contributes to the intensity enhancement of the blue tail of the spectrum. Regarding the solvated structure of the free electron, we have found that if the basis center is used as the electron site to calculate the correlation functions, the results predict a structure where the electron places itself on top of a central water molecule surrounded by the remaining water molecules in a very organized and stable arrangement. However, if the maximum of the electron density is used as electron site the obtained picture shows an electron located in a very fluctuating cavity that collapses and reforms continuously.

AB - In the current work, in order to model a free electron solvated in water, we have implemented a method to represent the molecular charge distribution as a set of Slater-type functions within the framework of a QM/MM method called QMSTAT. Also, it has been introduced in this method a new approach to calculate the intermolecular induction energy in the presence of very strong electric fields. Unlike most previous potentials, our method uses the ab initio energies of the electron-water complex as reference to obtain the few fitted parameters that the model needs, instead of the ab initio potential of the electron. A Metropolis-Monte Carlo simulation of 15 million steps has been carried out in a system that consists of an electron solvated in 200 water molecules explicitly described. The obtained results predict a vertical electron detachment energy of 3.30 eV and a radius of gyration of 2.38 Å, which are in very good agreement with the experimental data of 3.27 ± 0.10 eV and 2.45 Å, respectively. We have also obtained the absorption spectrum of the hydrated electron from our simulation. The maximum of the spectrum agrees very well with the experimental result and the experimental width at half-maximum is only 0.11 eV wider than the calculated curve. The calculations predict the same blue tail as the experimental result but with a less smooth shape. Also, our results indicate that the transfer of intensity from the transition arriving to the highest of the three p states to transitions arriving to higher-lying states contributes to the intensity enhancement of the blue tail of the spectrum. Regarding the solvated structure of the free electron, we have found that if the basis center is used as the electron site to calculate the correlation functions, the results predict a structure where the electron places itself on top of a central water molecule surrounded by the remaining water molecules in a very organized and stable arrangement. However, if the maximum of the electron density is used as electron site the obtained picture shows an electron located in a very fluctuating cavity that collapses and reforms continuously.

KW - Monte Carlo

KW - Non-linear polarization

KW - Penetration effects

KW - QM/MM

KW - Solvated electron

U2 - 10.1016/j.molliq.2019.111300

DO - 10.1016/j.molliq.2019.111300

M3 - Article

AN - SCOPUS:85069707153

SN - 0167-7322

VL - 292

JO - Journal of Molecular Liquids

JF - Journal of Molecular Liquids

IS - Oct

M1 - 111300

ER -