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Commonly-Used Program Options
A number of commonly-used program options are provided below. These are specified using keywords input into the Options box in the Calculations dialog. Keywords are case insensitive. An equals sign ("=") separates a keyword from its integer, real or character string value. Real values can optionally include an "e" floating point power of ten. Default values for keywords are indicated in bold, and alternative values in italics. A complete listing of supported keyword options is available as Appendix C in the Spartan Manual. |
| Conformational Searching Keywords associated with the Conformational Searching are as follows: |
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| keyword |
value
|
description |
|
|
||
| SEARCHMETHOD |
C
|
conformational searching method employed; overrides default choice
which depends on complexity of system (systematic methods are applicable
to systems with only a few degrees of conformational freedom) may be
overridden with one of the following: |
| MAXCONFS |
N
|
set maximum number of conformers to N; the program attempts to select the most diverse set (based on geometry) representing the entire population; default is 100 |
| WINDOW |
F
|
sets the maximum energy (in kcal/mol) at which a conformer will be kept to (minimum energy + F), where minimum energy is the energy of the lowest energy conformer encountered at that point in the search; default is 10 kcal/mol |
| MAXITR |
N
|
sets the number of iterations allowed for a Monte Carlo search (only) to N; default is a function of the number of conformational degrees of freedom |
| STARTTEMPERATURE |
F
|
sets initial "temperature" (in K) for a Monte Carlo search (only) to F; high temperatures will result in the molecule further "exploring" global space, while low temperatures will result in the molecule further "exploring" local space; default is 5000K |
| Geometry and Transition-State
Geometry Optimization Keywords associated with geometry optimization (all methods) and transition-state geometry optimization (quantum chemical methods only) are as follows: |
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| keyword |
value
|
description | ||||||||||||
|
|
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| GEOMETRYCYCLE |
N
|
set maximum number of equilibrium and transition-state geometry optimization cycles to N; default is number of independent variables +20 for equilibrium geometry optimization and 3x number of independent variables for transition-state geometry optimization | ||||||||||||
| GRADIENTTOLERANCE |
F
|
set convergence criterion in equilibrium and transition-state) geometry optimization for the maximum gradient component (in hartrees/bohr) to F; default is 4.5 x 10-4 | ||||||||||||
| DISTANCETOLERANCE |
F
|
set convergence criterion in equilibrium and transition-state geometry optimization for the maximum change in a bond length (in ) to F ; default is 1.8 x 10-3 | ||||||||||||
| HESS |
C
|
choose Hessian (matrix of second derivatives) for
start of geometry (transition-state geometry) optimization (in the absence
of a Hessian from a previous calculation, the default is MMFF molecular
mechanics for equilibrium geometry optimization and PM3 semi-empirical
for transition-state geometry optimization; may be overridden with one of the
following:
|
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| Quantum Chemical Calculations Keywords associated with all quantum chemical calculations are as follows: |
||||||||
| keyword |
value
|
description | ||||||
|
|
||||||||
| DIIS |
N
|
switch on diis all the time in SCF procedure. N is the size of the iterative subspace; it should be an integer between 2 and 10; default is 5 | ||||||
| NODIIS | turn off diis SCF convergence accelerator | |||||||
| ENERGY |
F
|
set SCF energy convergence criterion (in hartrees) to F; default is 1.0 x 10-6 | ||||||
| SCFCYCLE |
N
|
set maximum number of SCF iterations to N; default is 50 |
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| GUESS |
C
|
choose initial wavefunction guess; in the absence of a guess
from a previous calculation, default is either sad or PM3 depending
on the calculation type, and may be overridden with one of the following:
|
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| SCF |
C
|
SCF procedure; default is restricted for closed-shell systems and unrestricted for open-shell systems, either of which may be specified for both closed and open-shell systems | ||||||
| CORE |
C
|
use frozen core approximation in Møller-Plesset and advanced correlated calculations ; default is frozen which may be changed to thawed | ||||||
| SCFTOLERANCE |
C
|
control of all tolerances in SCF procedure; default is normal which may be changed to high or veryhigh | ||||||
| MIX |
–
|
specifies that the a and b HOMO's in the guess wavefunction
should be constructed according to: HOMOa=HOMO+LUMO/sqrt(2) HOMOb=HOMO+LUMO/sqrt(2) useful for generating a guess wavefunction for singlet diradical |
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| SMALLMEMORY |
–
|
disable use of fast "in memory" Hartree-Fock method | ||||||
| PRINTCOORDS |
–
|
prints Cartesian coordinates | ||||||
| PRINTLEV |
C
|
print level; default is normal which may be changed to verbose or debug | ||||||
| Semi-Empirical Calculations Keywords unique to semi-empirical calculations are as follows: |
||
| keyword |
value
|
description |
|
|
||
| NOSPEUDO |
–
|
turn off pseudodiagonalization in response to convergence difficulties |
| NOAMIDEFIX |
–
|
do not include the molecular mechanics amide correction in PM3 calculations (only) |
| HHOFF |
–
|
turns off hydrogen-hydrogen repulsion term in PM3 calculations; default only where no transition metals are involved for compatibility with "standard" PM3 |
| HHON |
–
|
turns on hydrogen-hydrogen repulsion term in PM3 calculations (only); default where transition metals are involved |
| INTENSITY |
–
|
obtain infrared intensities |
| Property Calculations Keywords associated with property calculations are as follows: |
||
| keyword |
value
|
description |
|
|
||
| NBO |
C
|
specify details of NBO population analysis; default is normal which may be overridden for ionic and 3C (three center) systems |
| ELCHARGE |
N
|
adjusts size of grid used to calculate charge from electrostatic potential; default is 1 point/atomic unit |
| TEMPERATURE |
F
|
temperature (in K) used in calculation of thermodynamic properties; default is 298°K |
| PRESSURE |
F
|
pressure (in atm) used in calculation of thermodynamic properties; default is 1 atm |
| MOMENTS |
–
|
calculates and prints principal moments of inertia |