Archive ouverte UNIGE | last documents for author 'Jakub Wojciech Kaminski'https://archive-ouverte.unige.ch/Latest objects deposited in the Archive ouverte UNIGE for author 'Jakub Wojciech Kaminski'engMulti-scale modelling of solvatochromic shifts from frozen-density embedding theory with non-uniform continuum model of the solvent: the coumarin 153 casehttps://archive-ouverte.unige.ch/unige:15943https://archive-ouverte.unige.ch/unige:15943For nine solvents of various polarity (from cyclohexane to water), the solvatochromic shifts of the lowest absorption band of coumarin 153 are evaluated using a computational method based on frozen-density embedding theory [Wesolowski and Warshel, J. Chem Phys., 1993, 97, 9050, and subsequent articles]. In the calculations, the average electron density of the solvent 〈ρB(r→)〉 is used as the frozen density. 〈ρB(r→)〉is evaluated using the statistical-mechanical approach introduced in Kaminski et al., J. Phys. Chem. A, 2010, 114, 6082. The small deviations between experimental and calculated solvatochromic shifts (the average deviation equals to about 0.02 eV), confirm the adequacy of the key approximations applied: (a) in the evaluation of the average effect of the solvent on the excitation energy, using the average density of the solvent instead of averaging the shifts over statistical ensemble and (b) using the approximant for the bi-functional of the non-electrostatic component of the orbital-free embedding potential, are adequate for chromophores which interact with the environment by non-covalent bonds. The qualitative analyses of the origin of the solvatochromic shifts are made using the graphical representation of the orbital-free embedding potential.Mon, 30 May 2011 15:34:59 +0200Orbital-free effective embedding potential at nuclear cuspshttps://archive-ouverte.unige.ch/unige:15002https://archive-ouverte.unige.ch/unige:15002A strategy to construct approximants to the kinetic-energy-functional dependent component (v[ρA,ρB](→r)) of the effective potential in one-electron equations for orbitals embedded in a frozen- density environment [Eqs. (20) and (21) in Wesolowski and Warshel, J. Phys. Chem. 97, (1993) 8050 ] is proposed. In order to improve the local behavior of the orbital-free effective embedding potential near nuclei in the environment, the exact behavior of vt[ρA,ρB](→r) at ρA→0 and ∫ρBd→r = 2 is taken into account. As a result, the properties depending on the quality of this potential are invariably improved compared to the ones obtained using conventional approximants which violated the considered exact condition. The approximants obtained following the proposed strategy and especially the simplest one constructed in this work are nondecomposable, i.e., cannot be used to obtain the analytic expression for the functional of the total kinetic energy.Mon, 18 Apr 2011 17:04:28 +0200Thermal Desorption, Vibrational Spectroscopic, and DFT Computational Studies of the Complex Manganese Borohydrides Mn(BH4)2 and [Mn(BH4)4]2−https://archive-ouverte.unige.ch/unige:14754https://archive-ouverte.unige.ch/unige:14754The mechanochemical reaction of LiBH4 with MnCl2 produces the neutral complex Mn(BH4)2. Thermal desorption studies show that the mechanochemical reaction of NaBH4 with MnCl2produces a different species, apparently Na2Mn(BH4)4, that undergoes dehydrogenation of a much lower weight percent H at a ~20 °C higher temperature than the neutral Mn(BH4)2. Vibrational spectroscopy also reveals that a complex manganese borohydride(s) in addition to Mn(BH4)2 are formed from the mechanochemical reactions. Analysis of the vibrational spectra in conjunction with DFT calculations on a model Mn(BH4)42− complex suggest bidentate binding of the [BH4]− ligands to the Mn center in the anionic complex. The calculated highest frequencies of the B−H stretching modes (corresponding to the "free" B−H bonds) agree well with the experimental frequencies and support the presence of this structural feature.Fri, 18 Mar 2011 15:07:53 +0100Modeling Solvatochromic Shifts Using the Orbital-Free Embedding Potential at Statistically Mechanically Averaged Solvent Densityhttps://archive-ouverte.unige.ch/unige:14717https://archive-ouverte.unige.ch/unige:14717The correspondence between the exact embedding potential and the pair of the electron densities—that of the embedded molecule and that of its environment [Wesolowski and Warshel, J. Phys. Chem. 1993, 97, 8050]—is used to generate the average embedding potential and to subsequently calculate the solvatochromic shifts in a number of organic chromophores in solvents of various polarities. The averaged embedding potential is evaluated at a fictitious electron density of the solvent, which is obtained by means of "dressing up" with electrons the classical site distributions derived from the statistical-mechanical, 3D molecular theory of solvation (aka 3D-RISM method) [Kovalenko In Molecular Theory of Solvation; Hirata, Ed.; Understanding Chemical Reactivity; 2003, Vol 24], self-consistently coupled with the electronic structure of the solute. The proposed approach to modeling solvatochromic shifts can be situated between the implicit and explicit type of models for the solvent. Numerical examples are given for the lowest-lying n → Π* and Π → Π* excitations.Fri, 18 Mar 2011 14:57:08 +0100Developement and applications of non-empirical methods for modelin electronic structure in condensed phasehttps://archive-ouverte.unige.ch/unige:8507https://archive-ouverte.unige.ch/unige:8507This thesis concerns new developments within the orbital-free embedding theory, improvement of the existing functionals and design of the new algorithms facilitating multi-level simulations in condensed phase. Orbital free-embedding formalism is a theoretical method formulated within Density Functional Theory (DFT) which is used to study the effect of the environment on the electronic structure of chemical species embedded in condensed phase. Its principal ingredient is universal exact orbital-free embedding potential, which is uniquely defined by the pair of electron densities, the one corresponding to the embedded system, and the one corresponding to its environment. In this thesis the properties of the embedding potential are studied. The new approximation to the relevant density functional is proposed. The new algorithm to perform geometry optimization within orbital-free embedding formalism is given and tested on the set of benchmark weakly bound intermolecular complexes. The linearization approximation to the embedding potential is proposed to reduce the time of calculations for the large systems. Finally the statistical-mechanical theory of the liquids is applied to generate the average density of the environment, which is used to obtain average embedding potential. The adequacy of multi-level modeling scheme with average embedding potential is verified on calculations of solvent shifts for various chromophores.Thu, 01 Jul 2010 13:39:24 +0200Cooperative effect of hydrogen-bonded chains in the environment of a π → π* chromophorehttps://archive-ouverte.unige.ch/unige:6178https://archive-ouverte.unige.ch/unige:6178Laser resonant two-photon ionization UV spectra provide clear evidence that the effect of increasing the length of the hydrogen-bonded chain consisting of molecules such as NH3, H2O, or CH3OH on the π → π* excitations of cis-7-hydroxyquinoline (cis-7HQ) is strongly cooperative [Thut; et al. J. Phys. Chem. A 2008, 112, 5566.] A theoretical analysis of the experimental data is provided to identify the origin of this cooperativity for four chains. The computational method to determine the changes of the electronic structure of a molecule due to interactions with its environment uses the nonempirical expression for the embedding potential [Wesolowski; Warshel J. Phys. Chem. 1993, 97, 8050.] It is concluded that the electronic coupling between the molecules at the ends of the chain, which are hydrogen-bonded to cis-7HQ, plays a crucial role in this cooperativity.Tue, 20 Apr 2010 12:09:25 +0200Equilibrium Geometries of Noncovalently Bound Intermolecular Complexes Derived from Subsystem Formulation of Density Functional Theoryhttps://archive-ouverte.unige.ch/unige:3593https://archive-ouverte.unige.ch/unige:3593The subsystem formulation of density functional theory is used to obtain equilibrium geometries and interaction energies for a representative set of noncovalently bound intermolecular complexes. The results are compared with literature benchmark data. The range of applicability of two considered approximations to the exchange-correlation- and nonadditive kinetic energy components of the total energy is determined. Local density approximation, which does not involve any empirical parameters, leads to excellent intermolecular equilibrium distances for hydrogen-bonded complexes (maximal error 0.13 Å for NH3−NH3). It is a method of choice for a wide class of weak intermolecular complexes including also dipole-bound and the ones formed by rare gas atoms or saturated hydrocarbons. The range of applicability of the chosen generalized gradient approximation, which was shown in our previous works to lead to good interaction energies in such complexes, where π-electrons are involved in the interaction, remains limited to this group because it improves neither binding energies nor equilibrium geometries in the wide class of complexes for which local density approximation is adequate. An efficient energy minimization procedure, in which optimization of the geometry and the electron density of each subsystem is made simultaneously, is proposed and tested.Fri, 02 Oct 2009 17:18:38 +0200LiSc(BH4)4: A Novel Salt of Li+ and Discrete Sc(BH4)4− Complex Anionshttps://archive-ouverte.unige.ch/unige:3567https://archive-ouverte.unige.ch/unige:3567LiSc(BH4)4 has been prepared by ball milling of LiBH4 and ScCl3. Vibrational spectroscopy indicates theFri, 02 Oct 2009 17:18:17 +0200Linearized orbital-free embedding potential in self-consistent calculationshttps://archive-ouverte.unige.ch/unige:3175https://archive-ouverte.unige.ch/unige:3175Conventionally, solving one-electron equations for embedded orbitals [Eqs. (20) and (21) in Wesolowski and Warshel, J Phys Chem, 1993, 97, 8050] proceeds by a self-consistent procedure in which the whole effective potential, including its embedding component, is updated in each iteration. We propose an alternative scheme (splitSCF), which uses the linearized embedding potential in the inner iterative loop and the outer-loop is used to account for its deviations from linearity. The convergence of the proposed scheme is investigated for a set of weakly bound intermolecular complexes representing typical interactions with the environment. The outer loop is shown to converge very fast. No more than 3-4 iterations are needed. Errors due to skipping the outer loop completely and using the electron density obtained in the absence of the environment in the linearized embedding potential are investigated in detail. It is shown that this computationally attractive simplification, used already in numerical simulations by others, is adequate not only for van der Waals and hydrogen-bonded complexes but even if the complex comprises charged components, i.e., where strong electronic polarization takes place. In charge-transfer type of complexes, larger changes of electron of density upon complex formation occur and the above simplification is not recommended.Mon, 21 Sep 2009 18:21:17 +0200The energy-differences based exact criterion for testing approximations to the functional for the kinetic energy of non-interacting electronshttps://archive-ouverte.unige.ch/unige:35https://archive-ouverte.unige.ch/unige:35abstract not availableWed, 29 Oct 2008 12:37:40 +0100