Charge Models#

Minimal Basis Iterative Stockholder (MBIS)#

The Minimal Basis Iterative Stockholder (MBIS) [Ayers2016] method is a variant of the Hirshfeld method. The idea behind this approach is to expand the pro-atomic density in a minimal set of atom-centered s-type Slater functions. MBIS is used in various applications like Force-Field parameterization or rescaling atomic polarizabilities.

MBIS charges can easily be requested by the simple input keyword MBIS:

!wB97X-V DEF2-TZVP MBIS

Within ORCA its also possible to compute atomic dipole-, quadrupole-, and octupolemoments within the MBIS scheme. These can be printed via the extended output option:

%method
MBIS_LARGEPRINT TRUE  # default = FALSE 
end

There are various further options to use with MBIS that can be found in the ORCA manual.

Example: 5,6-diaminobenzene-2,3-dicarbonitrile#

In this example, we will compute MBIS properties for 5,6-diaminobenzene-2,3-dicarbonitrile. This molecules has, for a neutral compound, a high experimental dipole moment of 10.5±0.2 Debye [Müllen2016].

../_images/mbis-example-2.png — Figure: Molecular structure of 5,6-diaminobenzene-2,3-dicarbonitrile.#

To obtain the MBIS charges and atomic multipoles we can employ the following input:

!wB97X-V DEF2-TZVP MBIS

%method
MBIS_LARGEPRINT TRUE  # default = FALSE
end

We can now find the MBIS charges in the output file basename.out:

------------------
MBIS ANALYSIS
------------------

Convergence threshold (charges)      ...        1.000e-06
Number of iterations                 ...        75

Total integrated alpha density       ...     40.999976141
Total integrated beta density        ...     40.999976141   

  ATOM     CHARGE    POPULATION     SPIN    
   0 N   -0.843167    7.843167    0.000000
   1 C    0.263784    5.736216    0.000000
   2 C    0.263771    5.736229    0.000000
   3 N   -0.843075    7.843075    0.000000
   4 C   -0.257113    6.257113    0.000000
   5 H    0.386416    0.613584    0.000000
   6 C   -0.027776    6.027776    0.000000
   7 C    0.356361    5.643639    0.000000
   8 C   -0.027781    6.027781    0.000000
   9 C    0.356301    5.643699    0.000000
  10 C   -0.257197    6.257197    0.000000
  11 H    0.386399    0.613601    0.000000
  12 H    0.384289    0.615711    0.000000
  13 N   -0.433371    7.433371    0.000000
  14 N   -0.433382    7.433382    0.000000
  15 H    0.384313    0.615687    0.000000
  16 H    0.170610    0.829390    0.000000
  17 H    0.170665    0.829335    0.000000

  TOTAL   0.000048   81.999952    0.000000

The charges mapped to to respective atoms are:

../_images/mbis-example-2-charges.png — Figure: MBIS charges mapped to the atoms in 5,6-diaminobenzene-2,3-dicarbonitrile.#

As we requested the large printout we also find the atomic dipole-

 MBIS ATOMIC DIPOLE MOMENT (A.U.):
  ATOM           X             Y             Z
   0 N      -0.038063     -0.015085     -0.103028
[...]

quadrupole-, and

 MBIS ATOMIC QUADRUPOLE MOMENT (A.U.):
  ATOM          XX            YY            ZZ            XY            XZ            YZ
   0 N      -5.193045     -5.361150     -5.246319     -0.051568      0.008765      0.095347
[...]

octupole moments

 MBIS ATOMIC OCTUPOLE MOMENT (A.U.):
  ATOM          XXX           YYY           ZZZ           XXY           XXZ           XYY           XYZ           XZZ           YYZ           YZZ
   0 N      -0.327968      0.057298     -0.069317     -0.055180     -0.039158     -0.006877      0.012999      0.314176     -0.394271     -0.035321
[...]

Note

Note that there are various other charge models available within ORCA including Mulliken, Hirshfeld, and more.

Charge Models#

Minimal Basis Iterative Stockholder (MBIS)#

Example: 5,6-diaminobenzene-2,3-dicarbonitrile#

Structures#