C.1 Q-Chem Text Input Summary

Keyword	Description
$molecule	Contains the molecular coordinate input (input file requisite).
$rem	Job specification and customization parameters (input file requisite).
$end	Terminates each keyword section.
$basis	User-defined basis set information (see Chapter 7).
$comment	User comments for inclusion into output file.
$ecp	User-defined effective core potentials (see Chapter 8).
$empirical_dispersion	User-defined van der Waals parameters for DFT dispersion
	correction.
$external_charges	External charges and their positions.
$force_field_params	Force field parameters for QM/MM calculations (see Section‘11.3).
$intracule	Intracule parameters (see Chapter 10).
$isotopes	Isotopic substitutions for vibrational calculations (see Chapter 10).
$localized_diabatization	Information for mixing together multiple adiabatic states into
	diabatic states (see Chapter 10).
$multipole_field	Details of a multipole field to apply.
$nbo	Natural Bond Orbital package.
$occupied	Guess orbitals to be occupied.
$opt	Constraint definitions for geometry optimizations.
$pcm	Special parameters for polarizable continuum models (see Section
	11.2.3).
$plots	Generate plotting information over a grid of points (see
	Chapter 10).
$qm_atoms	Specify the QM region for QM/MM calculations (see Section 11.3).
$solvent	Additional parameters and variables for implicit solvent models (see Section 11.2).
$svp	Special parameters for the SS(V)PE module.
$svpirf	Initial guess for SS(V)PE) module.
$van_der_waals	User-defined atomic radii for Langevin dipoles solvation (see
	Chapter 10).
$xc_functional	Details of user-defined DFT exchange-correlation functionals.
$cdft	Special options for the constrained DFT method as implemented.
$efp_fragments	Specifies labels and positions of EFP fragments.
$efp_params	Contains user-defined parameters for effective fragments.
$eom_user_guess	Contains user-defined guess for EOM-CC calculations.
$complex_ccman	Contains parameters for complex-scaled and CAP-augmented EOM-CC calculations.

Table C.1: Q-Chem user input section keywords. See the $QC/samples directory with your release for specific examples of Q-Chem input using these keywords.

Note: (1) Users are able to enter keyword sections in any order.
(2) Each keyword section must be terminated with the $end keyword.
(3) Not all keywords have to be entered, but $rem and $molecule are compulsory.
(4) Each keyword section will be described below.
(5) The entire Q-Chem input is case–insensitive.
(6) Multiple jobs are separated by the string @@@ on a single line.

C.1.1 Keyword: $molecule

Four methods are available for inputing geometry information:

Z-matrix (Angstroms and degrees):
$molecule
{Z-matrix}
{blank line, if parameters are being used}
{Z-matrix parameters, if used}
$end
Cartesian Coordinates (Angstroms):
$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

C.1.2 Keyword: $rem

See also the list of $rem variables at the end of this Appendix. The general format is:

$rem
   REM_VARIABLE   VALUE   [optional comment]
$end

C.1.3 Keyword: $basis

The format for the user–defined basis section is as follows:

$basis

$X$

0

$L$

$K$

$scale$

$\alpha _1$

$C_1^{L_{min}}$

$C_1^{L_{min}+1}$

$\ldots$

$C_1^{L_{max}}$

$\alpha _2$

$C_2^{L_{min}}$

$C_2^{L_{min}+1}$

$\ldots$

$C_2^{L_{max}}$

$\vdots$

$\vdots$

$\vdots$

$\ddots$

$\vdots$

$\alpha _ K$

$C_ K^{L_{min}}$

$C_ K^{L_{min}+1}$

$\ldots$

$C_ K^{L_{max}}$

****

$end

where

$X$	Atomic symbol of the atom (atomic number not accepted)
$L$	Angular momentum symbol (S, P, SP, D, F, G)
$K$	Degree of contraction of the shell (integer)
$scale$	Scaling to be applied to exponents (default is 1.00)
$a_ i$	Gaussian primitive exponent (positive real number)
$C_ i^ L$	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 Q-Chem input deck information, all input is case–insensitive.

C.1.4 Keyword: $comment

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

C.1.5 Keyword: $ecp

$ecp
For each atom that will bear an ECP
Chemical symbol for the atom
ECP name; the $L$ value for the ECP; number of core electrons removed
For each ECP component (in the order unprojected, $\hat{P}_0$ , $\hat{P}_1$ , , $\hat{P}_{L-1}$
The component name
The number of Gaussians in the component
For each Gaussian in the component
The power of $r$ ; the exponent; the contraction coefficient
****
$end

Note: (1) All of the information in the $ecp block is case–insensitive.
(2) The $L$ value may not exceed 4. That is, nothing beyond $G$ projectors is allowed.
(3) The power of $r$ (which includes the Jacobian $r^2$ factor) must be 0, 1 or 2.

C.1.6 Keyword: $empirical_dispersion

$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.

C.1.7 Keyword: $external_charges

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 Angstroms (the default), the coordinates for external charges should also be in Angstroms. If the structure is specified in atomic units, the coordinates for external charges should also be in atomic units. (See INPUT_BOHR.)

$external_charges
   x-coord1   y-coord1   z-coord1   charge1
   x-coord2   y-coord2   z-coord2   charge2
$end

C.1.8 Keyword: $intracule

$intracule

int_type

0

Compute $P(u)$ only

1

Compute $M(v)$ only

2

Compute $W(u,v)$ only

3

Compute $P(u)$ , $M(v)$ and $W(u,v)$

4

Compute $P(u)$ and $M(v)$

5

Compute $P(u)$ and $W(u,v)$

6

Compute $M(v)$ and $W(u,v)$

u_points

Number of points, start, end.

v_points

Number of points, start, end.

moments

0–4

Order of moments to be computed ( $P(u)$ only).

derivs

0–4

order of derivatives to be computed ( $P(u)$ only).

accuracy

$n$

( $10^{-n})$ specify accuracy of intracule interpolation table ( $P(u)$ only).

$end

C.1.9 Keyword: $isotopes

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

C.1.10 Keyword: $multipole_field

Multipole fields are all in atomic units.

$multipole_field
   field_component1   value1
   field_component2   value2
   ...
$end

C.1.11 Keyword: $nbo

Refer to Chapter 10 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

C.1.12 Keyword: $occupied

$occupied
   1  2  3  4 ...  nalpha
   1  2  3  4 ...  nbeta  
$end

C.1.13 Keyword: $opt

Note that units are in Angstroms 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

C.1.14 Keyword: $svp

$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

C.1.15 Keyword: $svpirf

 
$svpirf
    <# point> <x point> <y point> <z point> <charge> <grid weight>
    <# point> <x normal> <y normal> <z normal>
$end

C.1.16 Keyword: $plots

$plots
One comment line
Specification of the 3–D mesh of points on 3 lines:
$N_ x\quad x_{\ensuremath{\mathrm{min}}}\quad x_{\ensuremath{\mathrm{max}}}$
$N_ y\quad y_{\ensuremath{\mathrm{min}}}\quad y_{\ensuremath{\mathrm{max}}}$
$N_ z\quad z_{\ensuremath{\mathrm{min}}}\quad z_{\ensuremath{\mathrm{max}}}$
A line with 4 integers indicating how many things to plot:
$N_{\ensuremath{\mathrm{MO}}}\quad N_{\ensuremath{\mathrm{Rho}}}\quad N_{\ensuremath{\mathrm{Trans}}}\quad N_{\ensuremath{\mathrm{DA}}}$
An optional line with the integer list of MO’s to evaluate (only if $N_{\ensuremath{\mathrm{MO}}} > 0$ )
MO(1)  MO(2) $\ldots$ MO( $N_{\ensuremath{\mathrm{MO}}}$ )
An optional line with the integer list of densities to evaluate (only if $N_{\ensuremath{\mathrm{Rho}}} > 0$ )
Rho(1)  Rho(2) $\ldots$ Rho( $N_{\ensuremath{\mathrm{Rho}}}$ )
An optional line with the integer list of transition densities (only if $N_{\ensuremath{\mathrm{Trans}}}> 0$ )
Trans(1)  Trans(2) $\ldots$ Trans( $N_{\ensuremath{\mathrm{Trans}}}$ )
An optional line with states for detachment/attachment densities (if $N_{\ensuremath{\mathrm{DA}}} > 0$ )
DA(1)  DA(2) $\ldots$ DA( $N_{\ensuremath{\mathrm{DA}}}$ )
$end

C.1.17 Keyword: $localized_diabatization

$plots
One comment line.
One line with an an array of adiabatic states to mix together.
$<adiabat1> \; \; \; \; \; \; <adiabat2> \; \; \; \; \; \; \; <adiabat3>$ $\ldots$
$end

Note: We count adiabatic states such that the first excited state is $<adiabat> = 1$ , the fifth is $<adiabat> = 5$ , and so forth.

C.1.18 Keyword $van_der_waals

Note: all radii are given in angstroms.

$van_der_waals
   1
   atomic_number   VdW_radius
$end

(alternative format)

$van_der_waals
   2
   sequential_atom_number   VdW_radius 
$end

C.1.19 Keyword: $xc_functional

$xc_functional
   X  exchange_symbol  coefficient
   X  exchange_symbol  coefficient
   ...
   C  correlation_symbol  coefficient
   C  correlation_symbol  coefficient
   ...
   K  coefficient
$end

`$basis`
	$X$	0
	$L$	$K$	$scale$
	$\alpha _1$	$C_1^{L_{min}}$	$C_1^{L_{min}+1}$	$\ldots$	$C_1^{L_{max}}$
	$\alpha _2$	$C_2^{L_{min}}$	$C_2^{L_{min}+1}$	$\ldots$	$C_2^{L_{max}}$
	$\vdots$	$\vdots$	$\vdots$	$\ddots$	$\vdots$
	$\alpha _ K$	$C_ K^{L_{min}}$	$C_ K^{L_{min}+1}$	$\ldots$	$C_ K^{L_{max}}$
`****`
`$end`

int_type	0	Compute $P(u)$ only
	1	Compute $M(v)$ only
	2	Compute $W(u,v)$ only
	3	Compute $P(u)$ , $M(v)$ and $W(u,v)$
	4	Compute $P(u)$ and $M(v)$
	5	Compute $P(u)$ and $W(u,v)$
	6	Compute $M(v)$ and $W(u,v)$
u_points		Number of points, start, end.
v_points		Number of points, start, end.
moments	0–4	Order of moments to be computed ( $P(u)$ only).
derivs	0–4	order of derivatives to be computed ( $P(u)$ only).
accuracy	$n$	( $10^{-n})$ specify accuracy of intracule interpolation table ( $P(u)$ only).