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].

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                 ...        74

Total integrated alpha density       ...     52.999978264
Total integrated beta density        ...     52.999978264

  ATOM     CHARGE    POPULATION     SPIN
   0 N   -0.843178    7.843178    0.000000
   1 C    0.263789    5.736211    0.000000
   2 C    0.263801    5.736199    0.000000
   3 N   -0.843087    7.843087    0.000000
   4 C   -0.257154    6.257154    0.000000
   5 H    0.386423    0.613577    0.000000
   6 C   -0.027760    6.027760    0.000000
   7 C    0.356352    5.643648    0.000000
   8 C   -0.027763    6.027763    0.000000
   9 C    0.356292    5.643708    0.000000
  10 C   -0.257237    6.257237    0.000000
  11 H    0.386406    0.613594    0.000000
  12 H    0.384292    0.615708    0.000000
  13 N   -0.433365    7.433365    0.000000
  14 N   -0.433376    7.433376    0.000000
  15 H    0.384314    0.615686    0.000000
  16 H    0.170620    0.829380    0.000000
  17 H    0.170678    0.829322    0.000000

  TOTAL   0.000048   81.999952    0.000000

The charges mapped to to respective atoms are:

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

 MBIS ATOMIC DIPOLE MOMENT (A.U.):
  ATOM           X             Y             Z
   0 N      -0.038066     -0.015118     -0.103029
[...]

quadrupole-, and

 MBIS ATOMIC QUADRUPOLE MOMENT (A.U.):
  ATOM          XX            YY            ZZ            XY            XZ            YZ
   0 N      -5.193059     -5.361218     -5.246343     -0.051584      0.008768      0.095351
[...]

octupole moments

 MBIS ATOMIC OCTUPOLE MOMENT (A.U.):
  ATOM          XXX           YYY           ZZZ           XXY           XXZ           XYY           XYZ           XZZ           YYZ           YZZ
   0 N      -0.327912      0.056948     -0.069312     -0.055253     -0.039152     -0.006909      0.012998      0.314205     -0.394240     -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#

Starting structure#