Tutorial -- Electron Paramagnetic Resonance A-tensor
Performing a parallel relativistic calculation of EPR hyperfine coupling constant (A-tensor) is a simple two-step process
respect --scf --inp=my-input-file --nt=4 --scratch=/path/to/scratch/directory respect --hfcc --inp=my-input-file --nt=4 --scratch=/path/to/scratch/directory
The first call of respect
with the argument --scf performs the self-consistent field (SCF) optimization of ground-state molecular orbitals, which is a necessary prerequisite for the following A-tensor calculation. The second call of respect
with the argument --hfcc actually performs the EPR A-tensor simulation.
The other arguments mandatory to respect
are
--inp
specifies a name of the input file;--nt
specifies the number of physical cores required for parallel execution;--scratch
specifies a path to the scratch directory.
The input file my-input-file.inp should contain the input block scf:
with some SCF-specific keywords, and the input block hfcc:
with some EPR A-tensor-specific keywords. A comprehensive list of all keywords can be found for SCF here and for EPR A-tensor here. A simple example of my-input-file.inp looks like
#SCF input block #4c Dirac-Kohn-Sham DFT (B3LYP) calculation of GaO molecule scf: geometry: Ga 0.000 0.000 0.000 O 0.000 0.000 1.744 method: mdks/b3lyp basis: ucc-pvdz charge: 0 multiplicity: 2 maxiterations: 30 nc-model: gauss #nuclear charge model #A-tensor input block hfcc: active-atoms: all #eval. A-tensor for all atoms nmm-model: point #nuclear magnetic moment model
As a final note, there are several important and worth-to-remember aspects associated with the input syntax, namely
the input is case-insensitive
This means that the program does not distinguish between uppercase and lowercase letters.the input is insensitive to the number of blank lines and/or comment lines
All comments begin with the number sign (#), can start anywhere on a line and continue until the end of the line.the input is compliant with the dictionary syntax of the YAML markup language
This means that each input line is represented either by a singleblock:
statement or by a simplekeyword:value
pair, such as
block1: keyword1: value1 keyword2: value2 ... block2: keyword3: value3 keyword4: value4 ... block3: keyword5: value5 keyword6: value6 ...
It is essential to remember that all members of one block:
are lines beginning at the same indentation level. Whitespace indentation is used to denote the block structure; however, tab characters are never allowed as indentation. The only exception to the YAML-based input syntax is the block geometry:
which utilizes a simple xyz format for the molecular geometry specification.
TIPS & TRICKS
Q: How to scale the speed of light in calculations of A-tensor?
Set the cscale:
option in the SCF calculation. The scaling value is then automatically transferred to the HFCC calculation.
Q: Is it possible to scale the spin-orbit (SO) interaction in calculations of A-tensor?
Yes. To scale the SO interaction set soscale:
option in the SCF calculation. This setting is then automatically transferred to the HFCC calculation.
Q: Is there a way to launch SCF and EPR calculations without the need to explicitly setup the scratch path by "--scratch=/path/to/scratch/directory"?
Yes, the argument "--scratch=/path/to/scratch/directory" can be saved to the file .respectrc in your home directory. If both the file and the command line argument exist, then ReSpect takes the scratch directory setting from the command line.
Latest Publications
Book chapter on relativistic real-time electron dynamics
Book chapter on relativistic theory of EPR and (p)NMR
Useful Links
Our Contacts
Department of Chemistry
UiT The Arctic University of Norway
Tromsø, NO-9037 Norway
Email: info@respectprogram.eu