:orphan:
.. index:: *ESR
.. _*ESR:
=====
\*ESR
=====
This section gives directives for the calculation of ESR/EPR parameters, g-tensors and Hyperfine Coupling tensors (HFC).
..
COMMENT. Following lines are from nmr.rst, however, LONDON is not implemented for *ESR yet. /Oct 2022
If common gauge origin (CGO) is used, i.e. :LONDON not specified,
then the user can define the gauge origin used for the external
magnetic field with :ref:`HAMILTONIAN_.GAUGEORIGIN` or :ref:`HAMILTONIAN_.GO ANG`
under :ref:`**HAMILTONIAN`.
If :ref:`NMR_.USECM` is specified then center-of-mass is used as gauge origin.
Default is (0, 0, 0).
General control statements
==========================
.. index:: .PRINT
.. _ESR_.PRINT:
.PRINT
------
Print level.
*Default:*
::
.PRINT
0
Definition of the multiplicity and CI
=====================================
.. index:: .MULTIP
.. _ESR_.MULTIP:
.MULTIP
-------
::
.MULTIP
2
*Default:* Doublet for an odd number of electrons, triplet for an even number of electrons.
.. index:: .CI ROOTS
.. _ESR_.CI ROOTS:
.CI ROOTS
---------
::
.CI ROOTS
5
*Default:* The multiplicity.
.. index:: .ESR CI
.. _ESR_.ESR CI:
.ESR CI
-------
Genreal specification of the ESR CI space with GAS, generalized active spaces.
For easier description they are divided in three groups:
RAS1-GAS spaces, defining max number of holes in the doubly occupied orbitals in the reference wave function;
RAS2-GAS, one "CAS" space with the open shells from the reference wave functions;
RAS3-GAS spaces, defining max number of electrons in the empty (virtual) orbitals in the refenece wave function.
*Default:* "RESOLVE", that is, CI in the open shell orbitals from the reference wave function.
*Example:* S, SD, and SDT from the occupied orbitals, S and SD to the empty orbitals. The RAS2-GAS space is defined implicitly by the reference wave function, typically and average-of-configurations (AOC) Hartree-Fock. The example is for a case with inversion symmetry, if no inversion symmetry there is only one set orbitals in each GAS space.
::
.ESR CI
3 2 ! 3 RAS1-GAS spaces and 2 RAS3-GAS spaces
1 ! max 1 hole in first RAS1-GAS space
2 2 ! 2 g and 2 u orbitals in RAS1-GAS
2 ! max 2 holes in second RAS1-GAS space
4 2 ! 4 g and 2 u orbitals in RAS1-GAS
3 ! max 3 holes in third and last RAS1-GAS space
4 1 ! 4 g and 1 u orbitals in RAS1-GAS
2 ! max 2 electrons in first RAS3-GAS space
4 1 ! 4 g and 1 u orbitals in RAS3-GAS
1 ! max 1 electron in second and last RAS3-GAS space
4 1 ! 4 g and 1 u orbitals in RAS3-GAS
.. index:: .THRCI
.. _ESR_.THRCI:
.THRCI
------
::
.THRCI
1.d-5
*Default:* 1.d-4 for ppt accuracy. Can also be modified with .G10PPM keyword.
.. index:: .G10PPM
.. _ESR_.G10PPM:
.G10PPM
-------
Converge CI for 10 ppm accuracy in g-tensor values, default is ppt accuracy.
.. index:: .STATE
.. _ESR_.STATE:
.STATE
------
The first CI root belonging to the multiplet of quasi-degenerate states.
For example, if the ground state is a non-degenerate singlet state (non-relativistically a spin singlet)
followed by the triplet state you want to study, then you should specify state no. 2 here.
*Default:*
::
.STATE
1
.. index:: .KR-CON
.. _ESR_.KR-CON:
.KR-CON
-------
Use Kramers conjugation for odd-number of electrons. For a doublet state this means the program only
needs to converge one CI state instead of two CI states - reduces the CI time with a factor 2.
Definition of additional properties
===================================
The g-tensor and HFC-tensors for all selectred nuclei are always calculated.
.. index:: .SELECT
.. _ESR_.SELECT:
.SELECT
-------
Select which nuclei to calculate HFC for. Default is *all*, which can be quite time-consumig if the molecule has many atoms.
(You cannot use :ref:`INTEGRALS_.SELECT` under :ref:`**INTEGRALS` if you use this keyword, they do the same thing.
It is included here for convenience.)
To select three nuclei, no. 3, 7, and 8:
::
.SELECT
3
3 7 8
..
**Advanced options**