Density functional theory for van der Waals complexes: Size matters
Published: Feb. 7, 2024
Over
the
past
25
years
there
has
been
remarkable
progress
towards
accurate
description
of
nonbonded
interactions
within
context
density
functional
theory
(DFT).
Various
methods
have
devised
to
capture
London
dispersion,
which
is
most
exacting
contribution
noncovalent
interactions;
these
strategies
include
both
new
functionals
as
well
ad
hoc
dispersion
corrections
existing
functionals.
At
present,
it
possible
compute
interaction
energies
for
small
van
der
Waals
complexes
(containing
~20
atoms)
an
accuracy
~0.5
kcal/mol,
using
a
range
dispersion-inclusive
DFT
that
are
reviewed
here.
Systematic
tests
reveal
consistency
across
different
methods,
at
least
dimers.
same
time,
magnitude
systematically
smaller
than
benchmark
because
some
resides
semilocal
exchange-correlation
functional,
in
manner
difficult
disentangle.
Despite
impressive
results
systems,
best
contemporary
afford
larger
errors
systems
with
>~
100
atoms,
approaching
3-5
kcal/mol
compared
ab
initio
benchmarks
total
energies,
although
themselves
uncertainties
this
size.
Errors
vary
widely
from
one
method
next,
no
discernible
systematic
trend.
Nanoscale
thus
represent
frontier
development
interactions.
Language: Английский
Advancing Non-Atom-Centered Basis Methods for More Accurate Interaction Energies: Benchmarks and Large-Scale Applications
The Journal of Physical Chemistry A,
Journal Year:
2024,
Volume and Issue:
unknown
Published: Nov. 18, 2024
Recent
advances
in
local
electron
correlation
approaches
have
enabled
the
relatively
routine
access
to
CCSD(T)
[that
is,
coupled
cluster
(CC)
with
single,
double,
and
perturbative
triple
excitations]
computations
for
molecules
of
a
hundred
or
more
atoms.
Here,
approaching
their
complete
basis
set
(CBS)
limit
becomes
challenging
due
extensive
superposition
errors,
often
necessitating
use
large
atomic
orbital
(AO)
sets
diffuse
functions.
we
study
potential
remedy
form
non-atom-centered
floating
orbitals
(FOs).
FOs
are
still
rarely
employed
even
small
practical
complication
defining
position,
number,
exponents,
etc.
The
most
frequently
used
FO
method
thus
simply
places
single
center
number
toward
middle
noncovalent
dimers;
however,
larger
complexes
can
soon
become
insufficient.
A
recent
alternative
uses
grid
centers
around
monomers
s
function
per
center,
which
is
currently
applicable
only
H,
C,
N,
O
build
on
above
advantages
mitigate
some
drawbacks
previous
by
using
layer
4-9
FOs/center
each
monomer.
Thus,
double
placed
between
interacting
subsystems.
When
extending
double-ζ
AO
this
FOs,
quality
conventional
augmented
triple-ζ
bases
be
reached
surpassed
less
orbitals,
leading
few
tenths
kcal/mol
errors
medium-sized
dimers.
This
good
performance
extends
(shown
here
up
72
atoms),
as
efficient
natural
(LNO)
4
match
our
LNO-CCSD(T)/CBS
reference
within
ca.
0.1
kcal/mol.
These
developments
introduce
methods
accurate
modeling
molecular
without
limitations
atom
types
further
accelerating
calculations,
like
LNO-CCSD(T).
Language: Английский
Eliminating imaginary vibrational frequencies in quantum-chemical cluster models of enzymatic active sites
Published: Feb. 9, 2024
In
constructing
finite
models
of
enzyme
active
sites
for
use
in
quantum-chemical
calculations,
atoms
at
the
periphery
model
system
are
often
constrained
to
prevent
structural
collapse
during
geometry
relaxation.
A
simple
fixed-atom
or
``coordinate
lock''
approach
is
commonly
employed
but
leads
undesirable
artifacts
including
appearance
small
imaginary
frequencies.
These
preclude
evaluation
finite-temperature
free
energy
corrections,
limiting
thermochemical
calculations
enthalpies
only.
Full-dimensional
vibrational
frequency
possible
by
replacing
constraints
with
harmonic
confining
potentials,
and
here
we
compare
that
an
alternative
strategy
which
contributions
Hessian
simply
omitted.
While
does
eliminate
frequencies,
it
tends
underestimate
both
zero-point
entropy,
addition
artificial
rigidity
already
introduced
constraints.
Harmonic
potentials
frequencies
provide
a
flexible
means
construct
can
be
used
unconstrained
relaxations.
Language: Английский
Assessing the domain-based local pair natural orbital (DLPNO) approximation for non-covalent interactions in sizable supramolecular complexes
Published: March 4, 2024
The
titular
DLPNO
approximation
has
become
a
de
facto
standard
for
extending
correlated
wave
function
models
to
large
molecular
systems
yet
its
fidelity
intermolecular
interaction
energies
not
been
thoroughly
vetted.
Non-covalent
are
sensitive
tails
of
the
electron
density,
involving
parts
that
far
from
nuclei
and
may
be
discarded
in
some
local
correlation
treatments.
Meanwhile,
accuracy
is
known
deteriorate
as
size
increases
questions
have
raised
regarding
benchmark
calculations
van
der
Waals
complexes.
Here,
we
test
at
level
second-order
Moller-Plesset
perturbation
theory
(MP2)
with
up
240
atoms,
which
canonical
MP2
can
performed
comparison.
For
small
dimers,
find
DLPNO-MP2
within
3%
values
but
quite
poor
larger
systems,
unless
results
extrapolated
limit
where
threshold
discarding
PNOs
taken
zero.
sequence
nanoscale
graphene
dimers
(C96H24)2,
agree
1%,
independent
system
size,
provided
basis
set
does
contain
diffuse
functions.
presence
functions
causes
oscillatory
behavior
PNO
threshold,
making
it
impossible
extrapolate
meaningful
way.
Language: Английский