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The merits of the frozen-density embedding scheme to model solvatochromic shifts
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10.1063/1.1858411
/content/aip/journal/jcp/122/9/10.1063/1.1858411
http://aip.metastore.ingenta.com/content/aip/journal/jcp/122/9/10.1063/1.1858411

Figures

Image of FIG. 1.
FIG. 1.

Example structure of acetone and its 88 nearest water molecules as obtained from a CPMD simulation, substructures of which have been used for a comparison of (partly) frozen-density embedding and supermolecule calculations.

Image of FIG. 2.
FIG. 2.

Excited states (SAOP/TZP/DZ) of acetone-water complexes with different numbers of water molecules. All water molecules have been explicitly taken into account in the TDDFT calculation (scheme A). The longer, dashed lines correspond to the and valence transitions.

Image of FIG. 3.
FIG. 3.

Excited states (SAOP/TZP/DZ) of acetone-water complexes with different numbers of water molecules. Two water molecules have been explicitly taken into account in the TDDFT calculation (except for the isolated molecule calculation), while all additional water molecules are included via the QM/QM embedding scheme (scheme B). The longer, dashed lines correspond to the and valence transitions.

Image of FIG. 4.
FIG. 4.

Excited states (SAOP/TZP/DZ) of acetone-water complexes with different numbers of water molecules. All water molecules are included via the QM/QM embedding scheme in the TDDFT calculation (scheme C). The longer, dashed lines correspond to the and valence transitions.

Image of FIG. 5.
FIG. 5.

Excitation energies (SAOP/TZP, LDA/DZ for the frozen part; energies in units of eV) of the valence excitations of acetone in water using the QM/QM embedding scheme for a snapshot from a CPMD simulation, from which subsystems with different numbers of water molecules have been extracted. The frozen density in all cases was constructed as a sum of densities of water fragments. For clusters with more than 100 water molecules, rigid water molecules where assumed for all but the 20 water molecules nearest to the embedded acetone. For the largest clusters, the number also includes some acetone molecules from neighboring cells of the CPMD simulation.

Image of FIG. 6.
FIG. 6.

Radial distribution function and integral from a MD simulation (GAFF/TIP3P) in comparison to a CPMD simulation of the same system. Top, O(carbonyl)–H(water) distribution function; bottom, O(carbonyl)–O(water) distribution function.

Image of FIG. 7.
FIG. 7.

Simulated (SAOP/TZP/DZ) absorption spectrum of acetone in water. Excitation energies have been calculated for snapshots from a CPMD simulation for acetone vapor (dashed line) or acetone in water (solid line), respectively; all water molecules within a radius of from the acetone molecule have been considered in the latter calculations, and have been treated in a frozen-density fashion. In total, 300 (vapor) or 220 (solution) configurations have been sampled. A Gaussian smearing of has been applied to the peaks in the spectrum. Additionally, the curves of a Gaussian fit to the simulated absorption bands are shown for the gas-phase (dotted line) or solvated (dashed-dotted line) molecule, respectively.

Tables

Generic image for table
Table I.

Excitation energies (SAOP/TZP; in units of eV) of the and valence excitations of acetone in water using the QM/QM embedding scheme for clusters with two water molecules (optimized structure) or 52 water molecules (structure from arbitrary snapshot of a MD simulation). (N.B. Due to the different structures, the 2 and 52 results are not comparable.) For the preparation of the frozen densities, either SAOP/TZP and LDA/TZP (two water molecules) or SAOP/DZ and LDA/DZ (52 water molecules) were applied in combination with different SCF convergence parameters (see text for explanation). Additionally, approximate densities from superpositions of molecular fragments (“mol. frags.”), either taking the sum of the fragment densities (“sumf.”) or the density obtained after one diagonalization of the Fock matrix based on these fragment densities (“diag.”) are employed.

Generic image for table
Table II.

Excitation energies (SAOP/TZP/DZ, LDA/DZ for the frozen part; energies in units of eV) of the and valence excitations of acetone in water using the QM/QM embedding scheme for a snapshot from a CPMD simulation, from which subsystems with different numbers of water molecules have been extracted. Scheme A, supermolecule calculations; scheme B, the two nearest water molecules are included in the embedded system, the other water molecules are frozen; scheme C, all water molecules are frozen. We also show the values for the optimized isolated structure for comparison. For the largest cluster with , the frozen density was constructed as a superposition of molecular densities, see text. For the cluster with , both methods to construct the density are compared.

Generic image for table
Table III.

Shifts in the excitation energies compared to the optimized structure of isolated acetone, calculated from the excitation energies obtained with schemes A, B, and C shown in Table II.

Generic image for table
Table IV.

Estimations of the solvent shift of acetone in water (compared to the vapor spectrum) using different ways to estimate the peak maxima. All energies given in units of eV. Also given is the number of configurations used to extract the values. The labels have the following meanings: mte, mean transition energy; avg, average transition energy; max, peak maximum in simulated spectrum; max, fit, peak maximum in Gaussian fit to simulated spectrum (recommended).

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/content/aip/journal/jcp/122/9/10.1063/1.1858411
2005-03-03
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: The merits of the frozen-density embedding scheme to model solvatochromic shifts
http://aip.metastore.ingenta.com/content/aip/journal/jcp/122/9/10.1063/1.1858411
10.1063/1.1858411
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