Tip

All input files can be downloaded: Files.

nddo

This option controls how to perform an NDDO (like AM1, PM3, etc.) calculation.

Options

charge

Value	An integer
Default	0

Define the total charge of the system.

spin2p1

Value	An integer
Default	1 for even number of electrons
	2 for odd number of electrons

Define the spin multiplicity of the system, i.e., \(2S+1\), where \(S\) is the spin of the system. For example, to consider the singlet and triplet state, one should set spin2p1 to 1 and 3, respectively.

max_it

Value	A non-negative integer
Default	150

Define the maximum number of SCF iteration.

print_MO

Print molecular orbital coefficients. Without this, only molecular orbital energies and occupancies are printed.

use_hcore

Use the core Hamiltonian matrix as the initial guess. Without this, the superposition of atomic NDDO densities is used as the initial guess.

print_level

Value	PrintNone for restricted SCF (alpha and beta orbitals are restricted to be identical)
	PrintEssentials for unrestricted SCF (alpha and beta orbitals are not necessarily identical)
	PrintDetails for unrestricted SCF (alpha and beta orbitals are not necessarily identical)
Default	PrintEssentials

The information printing level.

density_cov

Value	A real number
Default	1.E-9

The density matrix convergence threshold for SCF calculations.

Theoretical Background

The NDDO (Neglect of Diatomic Differential Overlap) method is a semi-empirical quantum chemistry method that simplifies the calculation of electronic structures in molecules. It is based on the Hartree-Fock theory but introduces several approximations to reduce computational cost while maintaining reasonable accuracy for many systems. The following NDDO-based methods are implemented in Qbics:

mndo

am1

am1d

rm1

pm3

pm3d

pm6

pmo

pmow

Input Examples

Note that, in all examples below, you can change energy to opt to do geometry optimization, or md to do molecular dynamics.

Example: NDDO Geometry Optimization of Congo Red Anion

We perform an NDDO geometry optimization of the Congo Red anion, which is of charge -2. The input file is as follows:

nddo-1.inp

mol
    N     -1.54332513     -2.09816265      1.04511234
    C     -1.24833878     -0.93106019      0.36508274
    C     -2.25957296     -0.07865002     -0.14856083
    N     -3.66148390     -0.29307361     -0.15493448
    N     -4.18863626     -1.27534731      0.37531946
    C     -5.60908641     -1.45451288      0.28158560
    C     -6.44457282     -0.83932131     -0.67188202
    C     -7.79728533     -1.15798249     -0.73630174
    C     -8.36065510     -2.08786360      0.14739783
    C     -9.77016879     -2.45880897      0.04894333
    C    -10.37218322     -2.63400200     -1.20423937
    C    -11.70230579     -3.02737161     -1.30728487
    C    -12.47656958     -3.25031163     -0.15160638
    N    -13.86557539     -3.62919999     -0.14487415
    N    -14.32966893     -4.17706047     -1.14625475
    C    -15.69877226     -4.57627884     -1.20899537
    C    -16.68973206     -4.15262107     -0.27475128
    C    -18.01024266     -4.49443901     -0.39532055
    S    -19.17268148     -3.86811281      0.81316397
    O    -19.75454266     -5.01617220      1.39840350
    O    -18.38630356     -3.10248890      1.70179250
    O    -20.10356966     -3.11120162      0.06462974
    C    -18.41112808     -5.32846881     -1.47222133
    C    -19.77910594     -5.71132399     -1.62198661
    C    -20.17834220     -6.53295026     -2.64390564
    C    -19.22910471     -7.02196171     -3.56998588
    C    -17.90832650     -6.66645352     -3.45632203
    C    -17.46190253     -5.80234089     -2.41478734
    C    -16.07656666     -5.41039373     -2.29229722
    N    -15.13888043     -5.91803387     -3.19440229
    C    -11.87474269     -3.05051931      1.11034028
    C    -10.54202081     -2.66675984      1.20101906
    C     -7.53790038     -2.67731355      1.11825020
    C     -6.18479683     -2.37215059      1.18838640
    C     -1.87591174      1.15335474     -0.77615212
    C     -0.57261374      1.52889060     -0.93591287
    S     -0.22263048      3.07410672     -1.76404123
    C      0.45596204      0.67936168     -0.44539542
    C      1.82678779      1.04190252     -0.60713363
    C      2.83356234      0.24415341     -0.12687164
    C      2.52009139     -0.95668533      0.54667961
    C      1.20940505     -1.33293101      0.71264279
    C      0.14025272     -0.53616115      0.21319920
    H     -2.46523916     -2.46286272      0.99215794
    H     -0.83173045     -2.78829762      1.08002006
    H     -6.03185765     -0.10143589     -1.37897310
    H     -8.43461236     -0.66688250     -1.48777738
    H     -9.78049223     -2.47062911     -2.11801307
    H    -12.14290958     -3.16255408     -2.30720734
    H    -16.38964262     -3.50879982      0.57744179
    H    -20.50886405     -5.32738427     -0.88397665
    H    -21.23309870     -6.82252491     -2.75059996
    H    -19.55988556     -7.69221994     -4.37548943
    H    -17.19714755     -7.08561026     -4.18243768
    H    -15.48438601     -6.05340540     -4.11792530
    H    -14.24364693     -5.48258085     -3.17857290
    H    -12.46209252     -3.20084844      2.03078572
    H    -10.08787943     -2.51709145      2.19260752
    H     -7.96893149     -3.40122514      1.82663096
    H     -5.56169201     -2.85401081      1.95772702
    H     -2.67308708      1.82553392     -1.15690810
    H      2.05510061      1.99022309     -1.12996590
    H      3.88606179      0.53247497     -0.25657336
    H      3.33326449     -1.58194610      0.94036557
    H      1.01518864     -2.26662032      1.25943530
    O     -1.49324251      3.61129258     -2.06889525
    O      0.51932929      3.83612909     -0.83254053
    O      0.53967816      2.71626705     -2.90040345
end

nddo
    charge -2
    spin2p1 1
end

task
    opt am1
end

You can also change am1 to pm3, pm6, etc. to use other NDDO methods listed in the table above. The final geometry is shown below: