Users are able to enter input sections in any order; see Table 3.1 for a complete list of input sections.
Each input section must be terminated with $end.
Not all input sections are required, but $rem and $molecule are compulsory.
The entire QChem input is caseinsensitive.
Multiple jobs are separated by the string @@@ on a single line.
Four methods are available for inputing geometry information:
Zmatrix (Ångstroms and degrees):
$molecule
{Zmatrix}
{blank line, if parameters are being used}
{Zmatrix parameters, if used}
$end
Cartesian Coordinates (Ångstroms):
$molecule
{Cartesian coordinates}
{blank line, if parameter are being used}
{Coordinate parameters, if used}
$end
Read from a previous calculation:
$molecule
read
$end
Read from a file:
$molecule
read filename
$end
See also the list of $rem variables at the end of this Appendix. The general format is:
$rem REM_VARIABLE VALUE [optional comment] $end
The format for the user–defined basis section is as follows:
where
$basis
0
****
$end

Atomic symbol of the atom (atomic number not accepted) 

Angular momentum symbol (S, P, SP, D, F, G) 

Degree of contraction of the shell (integer) 

Scaling to be applied to exponents (default is 1.00) 

Gaussian primitive exponent (positive real number) 

Contraction coefficient for each angular momentum (non–zero real numbers). 
Atoms are terminated with **** and the complete basis set is terminated with the $end keyword terminator. No blank lines can be incorporated within the general basis set input. Note that more than one contraction coefficient per line is one required for compound shells like SP. As with all QChem input deck information, all input is case–insensitive.
Note that the entire input deck is echoed to the output file, thus making the $comment keyword largely redundant.
$comment User comments  copied to output file $end
$ecp
For each atom that will bear an ECP
Chemical symbol for the atom
ECP name; the value for the ECP; number of core electrons removed
For each ECP component (in the order unprojected, , , ,
The component name
The number of Gaussians in the component
For each Gaussian in the component
The power of ; the exponent; the contraction coefficient
****
$end
Note: (1) All of the information in the $ecp block is case–insensitive.
(2) The value may not exceed 4. That is, nothing beyond projectors is allowed.
(3) The power of (which includes the Jacobian factor) must be 0, 1 or 2.
$empirical_dispersion S6 S6_value D D_value C6 element_1 C6_value_for_element_1 element_2 C6_value_for_element_2 VDW_RADII element_1 radii_for_element_1 element_2 radii_for_element_2 $end
Note: This section is only for values that the user wants to change from the default values recommended by Grimme.
All input should be given in atomic units.
Update: While charges should indeed be listed in atomic units, the units for distances depend on the user input. If the structure is specified in Ångstroms (the default), the coordinates for external charges should also be in Ångstroms. If the structure is specified in atomic units, the coordinates for external charges should also be in atomic units. (See INPUT_BOHR.)
$external_charges xcoord1 ycoord1 zcoord1 charge1 xcoord2 ycoord2 zcoord2 charge2 $end
$intracule
$end
int_type
0
Compute only
1
Compute only
2
Compute only
3
Compute , and
4
Compute and
5
Compute and
6
Compute and
u_points
Number of points, start, end.
v_points
Number of points, start, end.
moments
0–4
Order of moments to be computed ( only).
derivs
0–4
order of derivatives to be computed ( only).
accuracy
( specify accuracy of intracule interpolation table ( only).
Note that masses should be given in atomic units.
$isotopes number_extra_loops tp_flag number_of_atoms [temp pressure] atom_number1 mass1 atom_number2 mass2 ... $end
Multipole fields are all in atomic units.
$multipole_field field_component1 value1 field_component2 value2 ... $end
Refer to Chapter 11 and the NBO manual for further information. Note that the NBO $rem variable must be set to ON to initiate the NBO package.
$nbo [ NBO options ] $end
$occupied 1 2 3 4 ... nalpha 1 2 3 4 ... nbeta $end
Note that units are in Ångstroms and degrees. Also see the summary in the next section of this Appendix.
$opt CONSTRAINT stre atom1 atom2 value ... bend atom1 atom2 atom3 value ... outp atom1 atom2 atom3 atom4 value ... tors atom1 atom2 atom3 atom4 value ... linc atom1 atom2 atom3 atom4 value ... linp atom1 atom2 atom3 atom4 value ... ENDCONSTRAINT FIXED atom coordinate_reference ... ENDFIXED DUMMY idum type list_length defining_list ... ENDDUMMY CONNECT atom list_length list ... ENDCONNECT $end
$svp <KEYWORD>=<VALUE>, <KEYWORD>=<VALUE>,... <KEYWORD>=<VALUE> $end
For example, the section may look like this:
$svp RHOISO=0.001, DIELST=78.39, NPTLEB=110 $end
$svpirf <# point> <x point> <y point> <z point> <charge> <grid weight> <# point> <x normal> <y normal> <z normal> $end
$plots
One comment line
Specification of the 3–D mesh of points on 3 lines:
A line with 4 integers indicating how many things to plot:
An optional line with the integer list of MO’s to evaluate (only if )
MO(1) MO(2) MO()
An optional line with the integer list of densities to evaluate (only if )
Rho(1) Rho(2) Rho()
An optional line with the integer list of transition densities (only if )
Trans(1) Trans(2) Trans()
An optional line with states for detachment/attachment densities (if )
DA(1) DA(2) DA()
$end
$plots
One comment line.
One line with an an array of adiabatic states to mix together.
$end
Note: We count adiabatic states such that the first excited state is , the fifth is , and so forth.
Note: All radii are given in Ångstroms.
$van_der_waals 1 atomic_number VdW_radius $end
(alternative format)
$van_der_waals 2 sequential_atom_number VdW_radius $end
$xc_functional X exchange_symbol coefficient X exchange_symbol coefficient ... C correlation_symbol coefficient C correlation_symbol coefficient ... K coefficient $end