13 research outputs found

### Accurate Modeling of Organic Molecular Crystals by Dispersion-Corrected Density Functional Tight Binding (DFTB)

The ambitious goal of organic crystal
structure prediction challenges
theoretical methods regarding their accuracy and efficiency. Dispersion-corrected
density functional theory (DFT-D) in principle is applicable, but
the computational demands, for example, to compute a huge number of
polymorphs, are too high. Here, we demonstrate that this task can
be carried out by a dispersion-corrected density functional tight
binding (DFTB) method. The semiempirical Hamiltonian with the D3 correction
can accurately and efficiently model both solid- and gas-phase inter-
and intramolecular interactions at a speed up of 2 orders of magnitude
compared to DFT-D. The mean absolute deviations for interaction (lattice)
energies for various databases are typically 2ā3 kcal/mol (10ā20%),
that is, only about two times larger than those for DFT-D. For zero-point
phonon energies, small deviations of <0.5 kcal/mol compared to
DFT-D are obtained

### Theoretical considerations from On the hydrogen activation by frustrated Lewis pairs in the solid state: benchmark studies and theoretical insights

Recently, the concept of small molecule activation by frustrated Lewis pairs (FLPs) has been expanded to the solid state showing a variety of interesting reactivities. Therefore, there is a need to establish a computational protocol to investigate such systems theoretically. In the present study, we selected several FLPs and applied multiple levels of theory, ranging from a semi-empirical tight-binding Hamiltonian to dispersion corrected hybrid density functionals. Their performance is benchmarked for the computation of crystal geometries, thermostatistical contributions, and reaction energies. We show that the computationally efficient HF-3c method gives accurate crystal structures and is numerically stable and sufficiently fast for routine applications. This method also gives reliable values for the thermostatistical contributions to Gibbs free energies. The meta-GGA TPSS-D3 evaluated in a projector augmented plane wave basis set is able to produce reaction electronic energies. The established protocol is intended to support experimental studies and to predict new reactions in the emerging field of solid-state FLPs

### Low-Cost Quantum Chemical Methods for Noncovalent Interactions

The efficient and reasonably accurate
description of noncovalent
interactions is important for various areas of chemistry, ranging
from supramolecular hostāguest complexes and biomolecular applications
to the challenging task of crystal structure prediction. While London
dispersion inclusive density functional theory (DFT-D) can be applied,
faster ālow-costā methods are required for large-scale
applications. In this Perspective, we present the state-of-the-art
of minimal basis set, semiempirical molecular-orbital-based methods.
Various levels of approximations are discussed based either on canonical
HartreeāFock or on semilocal density functionals. The performance
for intermolecular interactions is examined on various small to large
molecular complexes and organic solids covering many different chemical
groups and interaction types. We put the accuracy of low-cost methods
into perspective by comparing with first-principle density functional
theory results. The mean unsigned deviations of binding energies from
reference data are typically 10ā30%, which is only two times
larger than those of DFT-D. In particular, for neutral or moderately
polar systems, many of the tested methods perform very well, while
at the same time, computational savings of up to 2 orders of magnitude
can be achieved

### Geometrical Correction for the Inter- and Intramolecular Basis Set Superposition Error in Periodic Density Functional Theory Calculations

We extend the previously developed
geometrical correction for the
inter- and intramolecular basis set superposition error (gCP) to periodic
density functional theory (DFT) calculations. We report gCP results
compared to those from the standard BoysāBernardi counterpoise
correction scheme and large basis set calculations. The applicability
of the method to molecular crystals as the main target is tested for
the benchmark set X23. It consists of 23 noncovalently bound crystals
as introduced by Johnson et al. (J. Chem. Phys. 2012, 137, 054103) and refined by Tkatchenko et
al. (J. Chem. Phys. 2013, 139, 024705). In order to accurately describe long-range electron correlation
effects, we use the standard atom-pairwise dispersion correction scheme
DFT-D3. We show that a combination of DFT energies with small atom-centered
basis sets, the D3 dispersion correction, and the gCP correction can
accurately describe van der Waals and hydrogen-bonded crystals. Mean
absolute deviations of the X23 sublimation energies can be reduced
by more than 70% and 80% for the standard functionals PBE and B3LYP,
respectively, to small residual mean absolute deviations of about
2 kcal/mol (corresponding to 13% of the average sublimation energy).
As a further test, we compute the interlayer interaction of graphite
for varying distances and obtain a good equilibrium distance and interaction
energy of 6.75 Ć
and ā43.0 meV/atom at the PBE-D3-gCP/SVP
level. We fit the gCP scheme for a recently developed pob-TZVP solid-state
basis set and obtain reasonable results for the X23 benchmark set
and the potential energy curve for water adsorption on a nickel (110)
surface

### An Enamine/HB(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> Adduct as a Dormant State in Frustrated Lewis Pair Chemistry

The
enamine piperidinocyclopentene reacts with HBĀ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> by formation of the C-Lewis base/B-Lewis
acid adduct <b>10</b>. It shows a zwitterionic iminium ion/hydridoborate
structure. However, this adduct formation is apparently reversible
and may generate the āinvisibleā frustrated Lewis pair <b>11</b> as a reactive intermediate by hydroboration of the enamine
Cī»C bond in an equilibrium situation at room temperature. Consequently,
the FLP <b>11</b> was trapped by typical FLP reactions, namely
by the reaction with dihydrogen to give the ammonium/hydridoborate <b>12</b>, the acetylene deprotonation products <b>13</b> and <b>14</b>, and simple borane adducts with pyridine (<b>15</b>) and with an isonitrile (<b>17</b>). The products <b>10</b> and <b>12</b>ā<b>15</b> and the isonitrile adduct <b>17</b> were characterized by X-ray diffraction. A DFT study determined
the thermodynamic features of the <b>10</b> ā <b>11</b> equilibrium and of a previously discussed reference system (<b>18</b> ā <b>19</b>) derived by reacting piperidinocyclohexene
with HBĀ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>

### An Enamine/HB(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> Adduct as a Dormant State in Frustrated Lewis Pair Chemistry

The
enamine piperidinocyclopentene reacts with HBĀ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> by formation of the C-Lewis base/B-Lewis
acid adduct <b>10</b>. It shows a zwitterionic iminium ion/hydridoborate
structure. However, this adduct formation is apparently reversible
and may generate the āinvisibleā frustrated Lewis pair <b>11</b> as a reactive intermediate by hydroboration of the enamine
Cī»C bond in an equilibrium situation at room temperature. Consequently,
the FLP <b>11</b> was trapped by typical FLP reactions, namely
by the reaction with dihydrogen to give the ammonium/hydridoborate <b>12</b>, the acetylene deprotonation products <b>13</b> and <b>14</b>, and simple borane adducts with pyridine (<b>15</b>) and with an isonitrile (<b>17</b>). The products <b>10</b> and <b>12</b>ā<b>15</b> and the isonitrile adduct <b>17</b> were characterized by X-ray diffraction. A DFT study determined
the thermodynamic features of the <b>10</b> ā <b>11</b> equilibrium and of a previously discussed reference system (<b>18</b> ā <b>19</b>) derived by reacting piperidinocyclohexene
with HBĀ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>

### An Enamine/HB(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> Adduct as a Dormant State in Frustrated Lewis Pair Chemistry

The
enamine piperidinocyclopentene reacts with HBĀ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> by formation of the C-Lewis base/B-Lewis
acid adduct <b>10</b>. It shows a zwitterionic iminium ion/hydridoborate
structure. However, this adduct formation is apparently reversible
and may generate the āinvisibleā frustrated Lewis pair <b>11</b> as a reactive intermediate by hydroboration of the enamine
Cī»C bond in an equilibrium situation at room temperature. Consequently,
the FLP <b>11</b> was trapped by typical FLP reactions, namely
by the reaction with dihydrogen to give the ammonium/hydridoborate <b>12</b>, the acetylene deprotonation products <b>13</b> and <b>14</b>, and simple borane adducts with pyridine (<b>15</b>) and with an isonitrile (<b>17</b>). The products <b>10</b> and <b>12</b>ā<b>15</b> and the isonitrile adduct <b>17</b> were characterized by X-ray diffraction. A DFT study determined
the thermodynamic features of the <b>10</b> ā <b>11</b> equilibrium and of a previously discussed reference system (<b>18</b> ā <b>19</b>) derived by reacting piperidinocyclohexene
with HBĀ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>