: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**