12 research outputs found
MP2-F12 Basis Set Convergence for the S66 Noncovalent Interactions Benchmark: Transferability of the Complementary Auxiliary Basis Set (CABS)
Complementary auxiliary basis sets for F12 explicitly correlated calculations
appear to be more transferable between orbital basis sets than has been
generally assumed. We also find that aVnZ-F12 basis sets, originally developed
with anionic systems in mind, appear to be superior for noncovalent
interactions as well, and propose a suitable CABS sequence for them.Comment: AIP Conference Proceedings, in press (ICCMSE-2017 proceedings), 4
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The cc-pV5Z-F12 basis set: reaching the basis set limit in explicitly correlated calculations
We have developed and benchmarked a new extended basis set for explicitly
correlated calculations, namely cc-pV5Z-F12. It is offered in two variants,
cc-pV5Z-F12 and cc- pV5Z-F12(rev2), the latter of which has additional basis
functions on hydrogen not present in the cc-pVnZ-F12 (n=D,T,Q) sequence.A large
uncontracted 'reference' basis set is used for benchmarking. cc-pVnZ-F12 (n=D,
T, Q, 5) is shown to be a convergent hierarchy. Especially the cc-
pV5Z-F12(rev2) basis set can yield the valence CCSD component of total
atomization energies (TAEs), without any extrapolation, to an accuracy normally
associated with aug-cc-pV{5,6}Z extrapolations. SCF components are functionally
at the basis set limit, while the MP2 limit can be approached to as little as
0.01 kcal/mol without extrapolation. The determination of (T) appears to be the
most difficult of the three components and cannot presently be accomplished
without extrapolation or scaling. (T) extrapolation from cc-pV{T,Q}Z-F12 basis
sets, combined with CCSD-F12b/cc-pV5Z-F12 calculations appears to be an
accurate combination for explicitly correlated thermochemistry. For accurate
work on noncovalent interactions, basis set superposition error with the
cc-pV5Z-F12 basis set is shown to be so small that counterpoise corrections can
be neglected for all but the most exacting purposes.Comment: Molecular Physics, in press (Nicholas C. Handy memorial issue). DOI
preassigne
The X40x10 Halogen Bonding Benchmark Revisited: Surprising Importance of (n-1)d Subvalence Correlation
We
have re-evaluated the X40x10 benchmark for halogen bonding using conventional
and explicitly correlated coupled cluster methods. For the aromatic dimers at
small separation, improved CCSD(T)–MP2 “high-level corrections” (HLCs) cause
substantial reductions in the dissociation energy. For the bromine and iodine species,
(n-1)d subvalence correlation increases dissociation energies, and turns out to
be more important for noncovalent interactions than is generally realized; ; (n-1)sp subvalence correlation is much less important. The (n-1)d subvalence term is dominated by core-valence correlation; with the smaller cc-pVDZ-F12-PP and cc-pVTZ-F12-PP basis sets, basis set convergence for the core-core contribution becomes sufficiently erratic that it may compromise results overall. The two factors conspire to generate discrepancies of up to 0.9 kcal/mol (0.16 kcal/mol RMS) between the original X40x10 data and the present revision.</p
The S66 noncovalent interactions benchmark reconsidered using explicitly correlated methods near the basis set limit
The
S66 benchmark for noncovalent interactions has been re-evaluated using
explicitly correlated methods with basis sets near the one-particle basis set
limit. It is found that post-MP2 “high-level corrections” are treated adequately
well using a combination of CCSD(F12*) with (aug-)cc-pVTZ-F12 basis sets on the
one hand, and (T) extrapolated from conventional CCSD(T)/heavy-aug-cc-pV{D,T}Z
on the other hand. Implications for earlier benchmarks on the larger S66x8
problem set in particular, and for accurate calculations on noncovalent
interactions in general, are discussed. At a slight cost in accuracy, (T) can
be considerably accelerated by using sano-V{D,T}Z+ basis sets, while
half-counterpoise CCSD(F12*)(T)/cc-pVDZ-F12 offers the best compromise between
accuracy and computational cost.</p
Denture base materials surface roughness changes in response to exposure to cigarette smoke in an in vitro experiment
Aim: Denture base materials were subjected to cigarette smoke for the purpose of determining their surface roughness. Materials and Methods: Polymethylmethacrylate and flexible denture base materials were used to manufacture 40 specimens for this study (20 for each). Each sample was randomly assigned to one of four groups: control, flexible, and heat-cured denture base material samples. The heat-cured denture material samples were the only ones that had been exposed to cigarette smoke (subgroup III). There was a control group for each group. For the smoke test groups, distilled water was utilised, whereas cigarette smoking was used for the water test groups. Each participant in the trial was exposed to six cigarettes in a specially created smoking area. Surface roughness differences between pre- and post-smoking samples were analysed using a profilometer. The data was analysed using a paired comparison and an independent comparison. Groupings differed significantly in their initial roughness and final roughness, according to results from a paired t-test. Conclusion: Surface harshness of tobacco-smoke-exposed specimens of both the intensity-restored and the adaptive dental replacement base materials was greater
The X40x10 Halogen Bonding Benchmark Revisited: Surprising Importance of (n-1)d Subvalence Correlation
<p>We
have re-evaluated the X40x10 benchmark for halogen bonding using conventional
and explicitly correlated coupled cluster methods. For the aromatic dimers at
small separation, improved CCSD(T)–MP2 “high-level corrections” (HLCs) cause
substantial reductions in the dissociation energy. For the bromine and iodine species,
(n-1)d subvalence correlation increases dissociation energies, and turns out to
be more important for noncovalent interactions than is generally realized; ; (n-1)sp subvalence correlation is much less important. The (n-1)d subvalence term is dominated by core-valence correlation; with the smaller cc-pVDZ-F12-PP and cc-pVTZ-F12-PP basis sets, basis set convergence for the core-core contribution becomes sufficiently erratic that it may compromise results overall. The two factors conspire to generate discrepancies of up to 0.9 kcal/mol (0.16 kcal/mol RMS) between the original X40x10 data and the present revision.</p
Folding and unfolding movements in a [2]pseudorotaxane
A new dibenzo[24]crown-8 derivative (1) was synthesized and functionalized with aromatic moieties such as naphthalene and coumarin units. These two fluorophores are known to form an effective FRET (Forster resonance energy transfer) pair, and this formed the basis for the design of this host crown ether derivative. Results of the steady-state and time-resolved fluorescence studies confirmed the resonance energy transfer between the donor naphthalene moiety and acceptor coumarin fragment, while NMR spectra and computational studies support a folded conformation for the uncomplexed crown ether 1. This was found to form an inclusion complex, a [2]pseudorotaxane type with imidazolium ion derivatives as the guest molecules with varying alkyl chain lengths ([C4mim]+ or [C10mim]+). The host crown ether (1) tends to adopt an open conformation on formation of the interwoven inclusion complex (1•[C4mim]+ or 1•[C10mim]+). This change in conformation, from the folded to a open one, was predicted by computational as well as 1H NMR studies and was confirmed by single crystal X-ray structure for one (1•[C4mim]+) of the two inclusion complexes. The increase in the effective distance between the naphthalene and coumarin moieties in the open conformation of these inclusion complexes was also supported by the decrease in the effective FRET process that was operational between naphthalene and coumarin moieties in the free molecule (1). Importantly, this inclusion complex formation was found to be reversible, and in the presence of a stronger base/polar solvent, such as triethyl amine/DMSO, the deprotonation/effective solvation of the cationic imidizolium ions ([C4mim]+ or [C10mim]+) resulted in decomplexation or dethreading with restoration of the original emission spectra for 1, which signifies the subsequent increase in the FRET process. Thus we could demonstrate that a molecular folding-unfolding type of movement in the crown ether derivative could be induced by chemical input as an imidazolium ion
Molecular Interactions, Proton Exchange, and Photoinduced Processes Prompted by an Inclusion Process and a [2]Pseudorotaxane Formation
Appropriate
design of the host and guest components allows formation
of a novel [2]pseudorotaxane complex with an interrupted photoinduced
electron transfer (PET)-coupled fluorescence resonance energy transfer
(FRET) response. This is the first example of an inclusion complex
with NO<sub>6</sub>-based azacrown ether as the host unit (H). Different
guest molecules (G1, G2, G3, and G4) with varying stopper size are
used for the studies. Unlike G1, G2, and G3, G4 with a relatively
bulkier stopper fails to form a [2]pseudorotaxane complex. Isothermal
titration microcalorimetry measurements reveal a systematic increase
in the association constant for H·G1, H·G2, and H·G3
with a change in the stopper size. Thermodynamic data suggest that
the formation of H·G1/H·G2/H·G3 is exclusively driven
by a large positive entropic gain (<i>T</i>Δ<i>S</i> = 19.69/26.80/21.81 kJ·mol<sup>–1</sup>),
while the enthalpy change is slightly negative for H·G1/H·G3
(−2.61/–1.97 kJ·mol<sup>–1</sup>) and slightly
positive for H·G2 (Δ<i>H</i> = 5.98 kJ·mol<sup>–1</sup>). For these three inclusion complexes, an interrupted
PET-coupled FRET response is observed with varying efficiency, which
is attributed to the subtle differences in acidity of the NH<sub>2</sub><sup>+</sup> unit of the guest molecules and thus the proton exchange
ability between the host and respective guest. This is substantiated
by the results of the computational studies