Restart is possible for all the SCF and coupled cluster solvers in eT.
To restart every part of a calculation,
the restart keyword can be specified in the
do section.
The restart information will then be read from file,
if eT finds the required files to restart a section.
Default start guesses will be used,
in case the files cannot be found.
The converged \(t\) amplitudes are used
as a starting guess for the ground state multipliers.
If available,
the converged right excited states are used for
the left excited states (and vice versa),
otherwise the orbital differences are used.
To improve the convergence behavior, one might want to restart a CC3 calculation from a converged CCSD calculation. The example below shows how CC3 excitation energies are calculated by restarting from a CCSD calculation.
The minimal input to obtain two right excited states with CCSD would look like this:
system
name: H2O He
charge: 0
end system
do
excited state
end do
method
hf
ccsd
end method
solver cc es
singlet states: 2
end solver cc es
geometry
basis: cc-pVDZ
H 0.86681 0.60144 5.00000
H -0.86681 0.60144 5.00000
O 0.00000 -0.07579 5.00000
He 0.10000 -0.02000 7.53000
end geometry
For the CC3 input the method section has to be changed from ccsd to cc3 and the global restart keyword needs to be added to the do section:
method
hf
cc3
end method
do
restart
excited state
end do
The first input will be saved as ccsd.inp and the second as cc3.inp.
There are two ways to restart using the launch script.
Both inputs can be handed to the launch script in the same call:
path/to/eT_launch.py ccsd.inp cc3.inp
At first ccsd.inp will be executed in the scratch directory,
directly followed by the execution of cc3.inp in the same scratch directory.
eT will find the restart information from CCSD,
as the same scratch directory is used for both inputs.
Alternatively,
ccsd.inp can be run first,
saving its restart information using the -save flag
and specifying a path,
see the eT_launch page for details.
path/to/eT_launch.py ccsd.inp -save ./
There will be a directory called ccsd_restart_files containing
the restart information after the calculation has finished,
because we used the submit directory as save directory.
To restart CC3 from these restart files we type the following command:
path/to/eT_launch.py cc3.inp -load ./ccsd_restart_files
The launch script will then copy the files from ccsd_restart_files
to the scratch directory and run cc3.inp.
The restart keyword can also be specified
in the sections of the respective solvers
if restart is only desired for specific parts of the calculation.
The sections with a restart keyword are:
If all restart keywords are set, the effect is the same as if the global restart keyword was specified.
For MLCC calculations, there are some special restart keywords that enter the mlcc section:
orbital restart
cnto restart and nto restart
The orbital restart keyword enables restart from partitioned orbitals
from a previous MLCC calculation.
Note
When the orbital restart keyword is used the orbital partitioning
is skipped and the orbitals on file are assumed to be suitable
for the restarted calculation.
The keyword is not necessary for general MLCC restart,
as the orbital partitioning step will yield the same orbitals
if the input for the orbitals is the same.
This keyword can be used in cases when this step is computationally expensive.
If CNTOs or NTOs/canonical are requested,
the cnto restart or nto restart keyword can be used to avoid
the lower level CC calculation necessary to construct these orbitals:
In that case,
the eigenvectors of \(\boldsymbol{M}\) and \(\boldsymbol{N}\)
(the CNTO/NTO transformation matrices) obtained in a previous
MLCC calculation are read from disk.
Note
The cnto restart and nto restart keywords are only referenced
if the orbital type is cnto/cnto-approx or nto-canonical,
respectively.
Restarting from eT v1.0 or v1.1 requires special care since the format of the restart files was changed.
However, the convert_v1.0_restart_files.py script in dev_tools
can convert old restart files to the new format.
The easiest way to do this is to use the -load-v1-0, --load-v1-0-restart-directory option
with eT_launch.py.
This will convert the old restart files and write them to scratch.
The calculation can then be restarted normally using the restart keywords.
Note
The sign convention of the orbitals was changed between v1.0 and v1.1.
When restarting coupled cluster calculations from v1.0,
the keyword skip must be used in the solver scf section
to ensure that the signs are consistent:
solver scf
skip
...
end solver scf
Warning
MLCC calculations cannot be restarted from v1.0 or v1.1.
It is also possible to convert the old files manually using the script.
python convert_v1_0_restart_files.py path/to/old/restart/directory path/to/new/restart/directory
The second path argument is optional. If it is not provided, a new restart directory will be created in the old.