Q-Chem

https://manual.q-chem.com/latest
Admin
Q-Chem is a comprehensive ab initio quantum chemistry software package that integrates a variety of...
Tokens:536,968
Snippets:4,559
Trust Score:9.6
Update:2 months ago
Show doc for...
Tokens:
Raw
### BCC2 Methodology Input Example

Source: https://manual.q-chem.com/latest/Ch6.S6.SS7.html

Example input file for running a BCC2 calculation in Q-Chem.

```text
$molecule
   1 2
   F
   H 1 1.001
$end

$rem
   UNRESTRICTED      TRUE
   JOBTYPE           SP
   EXCHANGE          HF
   GEN_SCFMAN_FINAL  TRUE
   DO_BCC2           3                run BCC2
   SCF_ALGORITHM     DIIS
   SCF_GUESS         GWH
   BASIS             sto-3g
   AUX_BASIS         rimp2-vdz
   SCF_CONVERGENCE   8
   THRESH            14
   PURECART          1111
   INTEGRAL_SYMMETRY FALSE
$end
```

--------------------------------

### Example .qchemrc File

Source: https://manual.q-chem.com/latest/sect_customization.html

A practical example of overriding default $rem settings for DIIS subspace size, convergence threshold, and SCF cycles.

```text
$rem
   DIIS_SUBSPACE_SIZE   5         Modify max DIIS subspace size
   THRESH               10        10**(-10) threshold
   MAX_SCF_CYCLES       100       More than the default of 50
$end
```

--------------------------------

### Example $svp Input Section

Source: https://manual.q-chem.com/latest/subsec_SS%28V%29PE.html

A concrete example of an $svp input section defining cavity and dielectric parameters.

```text
$svp
   RHOISO=0.001, DIELST=78.39, NPTLEB=110
$end
```

--------------------------------

### OVOCV OO-DFT Analysis Input Example

Source: https://manual.q-chem.com/latest/sect_ovocv-analysis.html

Example input for performing OVOCV analysis on a charge transfer system, including initial data generation and subsequent excitation analysis.

```Q-Chem
$molecule
0 1
N     0.000000000     0.000000000     -2.149985070
H     -0.469826010     -0.813762490     -2.534400940
H     -0.469826010     0.813762490     -2.534400940
H     0.939652030     0.000000000     -2.534400940
F     0.000000000     0.000000000     15.850014930
F     0.000000000     0.000000000     17.275484090
$end

$comment
IMOM we use for TRIPLET EXCITATIONS or MIXED-SPIN configurations
$end

$rem
thresh              14
scf_convergence     8
method              hf
basis               def2-TZVP
scf_algorithm       diis_gdm
sym_ignore          true   #make sure symmetry is off
symmetry            false
XC_GRID             50000194
unrestricted        true
ovocv_analysis      1
save_ovocv_init_data 1
$end

@@@

$rem
unrestricted        true
thresh              14
scf_convergence     6
method              hf
basis               def2-TZVP
mom_method          imom
mom_start           1
scf_guess           read
scf_max_cycles      500
sym_ignore          true
symmetry            false
XC_GRID             50000194
make_cube_files     true
plots               1
ovocv_analysis      1
load_ovocv_init_data 1
ovocv_quadrature    9
ovocv_thresh        15000
ovocv_excite_analysis 1
ovocv_excite_type     1
save_ovocv            0
$end

$molecule
read
$end

$occupied
1 2 3 4 5 6 7 8 9 10 11 12 13 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14
$end

$plots
grid_points 50 50 50
$end
```

--------------------------------

### Interactive Input for input-Q-Chem-t-rex.sh

Source: https://manual.q-chem.com/latest/sect_Romberg.html

Example session for generating finite-field input files.

```text
Components: x=1 y=2 z=3 all_beta=4 all_alpha=5
4
File name
eth-
Number of field amplitudes
5
Smallest field amplitude F_0
0.0004
a   (F_k=a^k F_0)
2.0
Number of files created         101
```

--------------------------------

### User-Defined Basis Set Input Example

Source: https://manual.q-chem.com/latest/Ch8.S4.SS3.html

Example of a complete Q-Chem input file defining a non-standard basis set with PURECART settings.

```text
$molecule
   0  1
   O
   H  O  oh
   H  O  oh  2  hoh

   oh  =   1.2
   hoh = 110.0
$end

$rem
   EXCHANGE   hf
   BASIS      gen      user-defined general basis
   BASIS2     sto-3g   sto-3g orbitals as initial guess
   PURECART   112      Cartesian d functions, pure f and g
$end

$basis
   H  0
   S  2  1.00
      1.30976    0.430129
      0.233136   0.678914
****
   O  0
   S  2  1.00
      49.9810    0.430129
      8.89659    0.678914
   SP 2  1.00
      1.94524    0.049472    0.511541
      0.49336    0.963782    0.612820
   D  1  1.00
      0.39000    1.000000
   F  1  1.00
      4.10000    1.000000
   G  1  1.00
      3.35000    1.000000
****
$end
```

--------------------------------

### Batch Job Input File Example

Source: https://manual.q-chem.com/latest/Ch3.S5.SS1.html

Demonstrates a sequence of three jobs: a geometry optimization, a frequency calculation using the previous geometry and MOs, and a higher-level single-point energy calculation.

```Q-Chem
$comment
   Optimize H-H at HF/6-31G*
$end

$molecule
   0 1
   H
   H  1  r

   r = 1.1
$end

$rem
   JOBTYPE       opt    Optimize the bond length
   METHOD        hf
   BASIS         6-31G*
$end

@@@

$comment
   Now calculate the frequency of H-H at the same level of theory.
$end

$molecule
   read
$end

$rem
   JOBTYPE       freq    Calculate vibrational frequency
   METHOD        hf
   BASIS         6-31G*
   SCF_GUESS     read    Read the MOs from disk
$end

@@@

$comment
  Now a single point calculation at at MP2/6-311G(d,p)//HF/6-31G*
$end

$molecule
   read
$end

$rem
   METHOD        mp2
   BASIS         6-311G(d,p)
$end
```

--------------------------------

### ALMO-MSDFT diabatization configuration

Source: https://manual.q-chem.com/latest/subsec_frag_diabat.html

Example of an ALMO-MSDFT calculation setup for an ethylene dimer system.

```Q-Chem
  C      0.000000    0.000000    0.000000
  C      1.332000    0.000000    0.000000
  H     -0.574301    0.000000   -0.928785
  H     -0.574301    0.000000    0.928785
  H      1.906301    0.000000    0.928785
  H      1.906301    0.000000   -0.928785
--
0 1
  C     -0.000000    4.000000    0.000000
  C      1.332000    4.000000   -0.000000
  H     -0.574301    4.000000    0.928785
  H     -0.574301    4.000000   -0.928785
  H      1.906301    4.000000   -0.928785
  H      1.906301    4.000000    0.928785
$end

$rem
   METHOD               PBE0
   BASIS                6-31+G(D)
   UNRESTRICTED         TRUE
   THRESH               14
   SCF_CONVERGENCE      8
   SCFMI_MODE           1
   FRGM_METHOD          STOLL
   FRAG_DIABAT_METHOD   ALMO_MSDFT
   INTEGRAL_SYMMETRY    FALSE
   POINT_GROUP_SYMMETRY FALSE
$end

$almo_coupling
  1  2
  0  1
  --
  0  1
  1  2
$end
```

--------------------------------

### Q-Chem input for energy and gradient calculations with occ-RI-K

Source: https://manual.q-chem.com/latest/subsec_occrik.html

Example input file demonstrating the configuration for energy and gradient calculations using the occ-RI-K method. Ensure RI_J is set to false as recommended.

```text
$molecule
   0   1
   C    0.0000000    0.3057430    5.7138876
   C    0.0000000   -0.5442831    4.4256275
   C    0.0000000    0.3675825    3.1787857
   C    0.0000000   -0.4853210    1.8908707
   C    0.0000000    0.4264823    0.6439435
   C    0.0000000   -0.4264823   -0.6439435
   C    0.0000000    0.4853210   -1.8908707
   C    0.0000000   -0.3675825   -3.1787857
   C    0.0000000    0.5442831   -4.4256275
   C    0.0000000   -0.3057430   -5.7138876
   H    0.8973039    0.9418895    5.7433715
   H   -0.8973039    0.9418895    5.7433715
   H   -0.8965960   -1.1827891    4.4155828
   H    0.8965960   -1.1827891    4.4155828
   H    0.8966512    1.0057416    3.1940146
   H   -0.8966512    1.0057416    3.1940146
   H   -0.8966512   -1.1234851    1.8761493
   H    0.8966512   -1.1234851    1.8761493
   H    0.8966507    1.0646443    0.6587590
   H   -0.8966507    1.0646443    0.6587590
   H   -0.8966507   -1.0646443   -0.6587590
   H    0.8966507   -1.0646443   -0.6587590
   H    0.8966512    1.1234851   -1.8761493
   H   -0.8966512    1.1234851   -1.8761493
   H   -0.8966512   -1.0057416   -3.1940146
   H    0.8966512   -1.0057416   -3.1940146
   H    0.8965960    1.1827891   -4.4155828
   H   -0.8965960    1.1827891   -4.4155828
   H    0.8973039   -0.9418895   -5.7433715
   H    0.0000000    0.3580832   -6.5913113
   H   -0.8973039   -0.9418895   -5.7433715
   H    0.0000000   -0.3580832    6.5913113
$end

$rem
   JOBTYPE         force
   EXCHANGE        HF
   BASIS           cc-pVTZ
   AUX_BASIS       cc-pVTZ-JK
   OCC_RI_K        1
   RI_K_GRAD       1
   INCFOCK         0
   PURECART        1111
$end
```

--------------------------------

### SQC/MM simulation input

Source: https://manual.q-chem.com/latest/sect_MMND.html

Example input for an SQC/MM nonadiabatic dynamics simulation starting on the S2 state with Wigner-sampled initial conditions.

```Q-Chem
$molecule
0 1
  C     -1.10077021     -0.38619733      0.05617695
  C      0.09675762     -1.08610723     -0.30779113
  C      1.28662554     -0.41739388     -0.28021086
  O      1.41824439      0.84326764      0.06159343
  O     -1.12106364      0.80448471      0.39946439
  H      0.49060260      1.16255871      0.27980893
  H      0.06099112     -2.12846061     -0.60005353
  H      2.23038546     -0.89206633     -0.54524306
  H     -2.05177379     -0.94757617      0.02607669
$end

$rem
   JOBTYPE                  freq
   METHOD                   pbe0
   BASIS                    6-31g*
$end

@@@

$molecule
read
$end

$rem
   JOBTYPE                 aimd
   METHOD                  pbe0
   BASIS                   6-31g*
   CIS_N_ROOTS             4
   CIS_SINGLETS            true
   CIS_TRIPLETS            false
   AIMD_METHOD             qcmd      !initiates quasi-classical nonadiabatic dynamics
   QCMD_METHOD             sqc
   TIME_STEP               10        !in atomic units
   AIMD_STEPS              340
   QCMD_INITSTATE          2         !start on S2
   QCMD_INITNUC            wigner    !sample from a Wigner distribution
   SQC_GAMADJUST           true
   AIMD_TEMP               0
   RPA                     0
$end
```

--------------------------------

### Ehrenfest simulation input

Source: https://manual.q-chem.com/latest/sect_MMND.html

Example input for an Ehrenfest nonadiabatic dynamics simulation starting on the S5 state with Boltzmann-sampled initial conditions.

```Q-Chem
$molecule
0 1
 Na      0.00000000      0.00000000      0.93444743
  H      0.00000000      0.00000000     -0.93444743
$end

$rem
   JOBTYPE                  freq
   METHOD                   hflyp
   BASIS                    6-31g*
$end

@@@

$molecule
   read
$end

$rem
   JOBTYPE                 aimd
   METHOD                  hflyp
   BASIS                   6-31g*
   CIS_N_ROOTS             6
   CIS_SINGLETS            true
   CIS_TRIPLETS            false
   AIMD_METHOD             qcmd      !initiates quasi-classical nonadiabatic dynamics
   QCMD_METHOD             ehrenfest
   TIME_STEP               10        !in atomic units
   AIMD_STEPS              340
   QCMD_INITSTATE          5         !start on S5
   QCMD_INITNUC            boltzmann !sample from a Boltzmann distribution
   AIMD_TEMP               300
   RPA                     0
$end
```

--------------------------------

### Triplet Excited State Geometry Optimization in Single-Precision

Source: https://manual.q-chem.com/latest/sec_SP_EOM_CC.html

Example of a geometry optimization for a triplet excited state of a uracil-water complex using a single-precision setup.

```Q-Chem
$molecule
   0 1
   N     0.034130    -.986909    0.000000
   N    -1.173397     .981920    0.000000
   C    -1.218805    -.408164    0.000000
   C    -0.007302    1.702153    0.000000
   C     1.196200    1.107045    0.000000
   C     1.289085    -.345905    0.000000
   O     2.310232    -.996874    0.000000
   O    -2.257041   -1.026495    0.000000
   H     0.049329   -1.997961    0.000000
   H    -2.070598    1.437050    0.000000
   H    -0.125651    2.776484    0.000000
   H     2.111671    1.674079    0.000000
   O     1.747914   -1.338382   -3.040233
   H     2.180817   -1.817552   -2.333676
   H     0.813180   -1.472188   -2.883392
$end

$rem
   JOB_TYPE              = opt
   METHOD                = ccsd
   BASIS                 = cc-pvdz
   CC_STATE_TO_OPT       = [1,1]
   MEM_TOTAL             = 30000
   EE_TRIPLETS           = [1]
   CC_SP_T_CONV          = 4
   CC_SP_E_CONV          = 6
   CC_SINGLE_PREC        = 1
   EOM_SINGLE_PREC       = 1
   CC_SP_DM              = 1
   CC_EOM_PROP           = 1
   EOM_ARESP_SINGLE_PREC = 1
$end
```

--------------------------------

### Basic QM/MM Optimization Input

Source: https://manual.q-chem.com/latest/sect_CHARMM.html

Example input file for a QM/MM optimization of a water dimer using the Q-Chem/Charmm interface.

```Q-Chem
$molecule
   0 1
   O    -0.91126   1.09227   1.02007
   H    -1.75684   1.51867   1.28260
   H    -0.55929   1.74495   0.36940
$end

$rem
   METHOD        hf        ! HF Exchange
   BASIS         cc-pvdz   ! Correlation Consistent Basis
   QM_MM         true      ! Turn on QM/MM calculation
   JOBTYPE       force     ! Need this for QM/MM optimizations
$end

$external_charges
   1.20426      -0.64330   0.79922  -0.83400
   1.01723      -1.36906   1.39217   0.41700
   0.43830      -0.06644   0.91277   0.41700
$end
```

--------------------------------

### SMD Model with User-Defined Solvent Configuration

Source: https://manual.q-chem.com/latest/ex_SMx-User-Solvent.html

Example input file demonstrating the use of the $smx section to define custom solvent parameters for the SMD model.

```Q-Chem
$comment
User-defined specification of pentane.
(Result should be equivalent to SOLVENT = PENTANE)
$end

$molecule
   0 1
   C    -0.361658    -0.986967     0.222366
   C    -1.331098     0.144597    -0.108363
   O    -0.592574     1.354183     0.036738
   C     0.798089     1.070899     0.136509
   C     0.964682    -0.396154    -0.256319
   H    -0.625676    -1.925862    -0.267011
   H    -0.333229    -1.158101     1.302753
   H    -1.697529     0.068518    -1.140448
   H    -2.193412     0.181620     0.562129
   H     1.130199     1.238399     1.169839
   H     1.348524     1.754318    -0.514697
   H     1.050613    -0.489646    -1.343151
   H     1.843065    -0.855802     0.199659
$end

$rem
   METHOD           b3lyp
   BASIS            6-31G*
   SOLVENT_METHOD   smd
$end

$smx
solvent other
epsilon 1.840
SolN    1.357
SolA    0.000  ! could be omitted
SolB    0.000  ! could be omitted
SolG   22.300
SolC    0.000  ! could be omitted
SolH    0.000  ! could be omitted
$end
```

--------------------------------

### CAP-AIMD Simulation Input

Source: https://manual.q-chem.com/latest/ex_CAP_HF_energy_decomp.html

Example input for an Ab Initio Molecular Dynamics (AIMD) simulation using a CAP. This setup includes velocity initialization and specific AIMD control parameters in the $rem section.

```Q-Chem
$molecule
 READ
$end

$velocity
3.6095e-05   4.1623e-06   2.3754e-05
-9.7386e-04  -1.4552e-05  -1.2310e-03
-2.8737e-04   1.2165e-04   2.9068e-04
3.3619e-05  -1.3939e-04   1.0849e-04
6.4312e-04   2.0187e-04  -4.2066e-04
-2.1196e-04   1.3012e-03  -2.1364e-04
$end

$rem
¯JOBTYPE¯¯AIMD
¯METHOD¯¯¯HF
¯BASIS¯¯¯GENERAL
¯GEN_SCFMAN¯¯TRUE
¯SKIP_OLD_SCFMAN¯TRUE
¯SCF_CONVERGENCE¯8
¯MAX_SCF_CYCLES¯¯3000
integral_symmetry FALSE
point_group_symmetry False
¯SCF_GUESS¯¯READ
¯COMPLEX_CCMAN¯¯TRUE
¯UNRESTRICTED¯¯TRUE
¯MOM_START¯¯1
¯MOM_METHOD¯¯MOM
¯TIME_STEP¯¯2
¯AIMD_STEPS¯¯200
   ¯FOCK_EXTRAP_ORDER      0
   ¯FOCK_EXTRAP_POINTS     0
  ¯AIMD_MOMENTS¯¯1
  ¯AIMD_PRINT¯¯2¯! Print Mulliken charges and dipole moments at each step
¯CS_STRICT¯¯TRUE
$end

$complex_ccman
¯CS_HF ¯¯¯1
¯CAP_TYPE ¯¯1
¯CAP_ETA ¯¯230
¯CAP_X ¯¯¯4360
¯CAP_Y ¯¯¯2680
¯CAP_Z ¯¯¯4360
$end

$basis
H¯0
cc-pvtz
****
C     0
S    8   1.00
   8236.0000000              0.0005310
   1235.0000000              0.0041080
    280.8000000              0.0210870
     79.2700000              0.0818530
     25.5900000              0.2348170
      8.9970000              0.4344010
      3.3190000              0.3461290
      0.3643000             -0.0089830
S    8   1.00
   8236.0000000             -0.0001130
   1235.0000000             -0.0008780
    280.8000000             -0.0045400
     79.2700000             -0.0181330
     25.5900000             -0.0557600
      8.9970000             -0.1268950
      3.3190000             -0.1703520
      0.3643000              0.5986840
S    1   1.00
     11.8760000              1.0000000
S    1   1.00
      4.2920000              1.0000000
S    1   1.00
      0.9059000              1.0000000
S    1   1.00
      0.1285000              1.0000000
P    3   1.00
     18.7100000              0.0140310
      4.1330000              0.0868660
      1.2000000              0.2902160
P    1   1.00
     33.1900000              1.0000000
P    1   1.00
      8.7780000              1.0000000
P    1   1.00
      0.3827000              1.0000000
P    1   1.00
      0.1209000              1.0000000
D    1   1.00
     14.8390000              1.0000000
D    1   1.00
      1.0970000              1.0000000
D    1   1.00
      0.3180000              1.0000000
F    1   1.00
      0.7610000              1.0000000
      P¯1¯¯1.00
      ¯¯0.06045¯1.00
      P¯1¯¯1.00
      ¯¯0.030225¯1.00
      P¯1¯¯1.00
      ¯¯0.0151125¯1.00
****
$end
```

--------------------------------

### Example of $plots input deck

Source: https://manual.q-chem.com/latest/sect_plot.mo.html

This input deck demonstrates evaluating the HOMO and LUMO of H2 on a 1x1x15 grid along the bond axis.

```Q-Chem
$molecule
   0  1
   H   0.0   0.0   0.35
   H   0.0   0.0  -0.35
$end

$rem
   METHOD     hf
   BASIS      6-31g**
   IANLTY     200
$end

$plots
   Plot the HOMO and the LUMO on a line
   1   0.0   0.0
   1   0.0   0.0
  15  -3.0   3.0
   2   0   0   0
   1   2
$end
```

--------------------------------

### OVOCV OO-DFT Analysis for LMCT in Fe(H2O)6 3+

Source: https://manual.q-chem.com/latest/sect_ovocv-analysis.html

This example demonstrates a multi-step workflow for OVOCV analysis, starting with initial data generation, followed by a fragment-based SCF guess, and concluding with excitation analysis.

```Q-Chem
$molecule
+3 6
--
+3 6
Fe     -0.5022247054     1.2927779200     0.0001938411
--
0 1
H       2.1134166395     2.0808631740    -0.0009010689
H      -0.5027205697    -1.3235141738    -0.7847973080
H      -3.1183219511     2.0796505928    -0.0004236834
H       0.2840444564     1.2933014045     2.6166394903
H      -0.5027751731     3.9101762183     0.7846214605
O       1.5358193871     1.2947592260    -0.0014374082
H       2.1156949943     0.5103151332    -0.0009786075
O      -0.5019595039     3.3312830798    -0.0005116891
H      -0.5019009551     3.9098531329    -0.7858415694
O      -0.5013746615     1.2930914301     2.0381118720
H      -1.2864874118     1.2932385232     2.6170717164
O      -2.5401948736     1.2938974534     0.0009627059
H      -3.1195714968     0.5090879007     0.0019042859
O      -0.5018840213    -0.7448372467     0.0005186723
H      -0.5008290080    -1.3235744599     0.7857827770
O      -0.5020354665     1.2915906981    -2.0378380237
H       0.2835925140     1.2915440728    -2.6160740707
H      -1.2869601935     1.2917959205    -2.6170203924
$end

$rem
jobtype             sp
method              wb97x-v
basis               def2-tzvp
scf_max_cycles      1000
scf_algorithm       gdm
sym_ignore          true
symmetry            false
thresh              14
scf_convergence     7
unrestricted        true
ovocv_analysis      1
save_ovocv_init_data 1
$end
```

```Q-Chem
$molecule
+3 6
--
+2 5
Fe     -0.5022247054     1.2927779200     0.0001938411
--
+1 2
H       2.1134166395     2.0808631740    -0.0009010689
H      -0.5027205697    -1.3235141738    -0.7847973080
H      -3.1183219511     2.0796505928    -0.0004236834
H       0.2840444564     1.2933014045     2.6166394903
H      -0.5027751731     3.9101762183     0.7846214605
O       1.5358193871     1.2947592260    -0.0014374082
H       2.1156949943     0.5103151332    -0.0009786075
O      -0.5019595039     3.3312830798    -0.0005116891
H      -0.5019009551     3.9098531329    -0.7858415694
O      -0.5013746615     1.2930914301     2.0381118720
H      -1.2864874118     1.2932385232     2.6170717164
O      -2.5401948736     1.2938974534     0.0009627059
H      -3.1195714968     0.5090879007     0.0019042859
O      -0.5018840213    -0.7448372467     0.0005186723
H      -0.5008290080    -1.3235744599     0.7857827770
O      -0.5020354665     1.2915906981    -2.0378380237
H       0.2835925140     1.2915440728    -2.6160740707
H      -1.2869601935     1.2917959205    -2.6170203924
$end

$rem
jobtype             sp
scf_guess           fragmo
FRGM_METHOD         STOLL
SCF_PRINT_FRGM      TRUE
method              wb97x-v
basis               def2-tzvp
scf_max_cycles      1000
scf_algorithm       gdm
sym_ignore          true
symmetry            false
thresh              14
scf_convergence     7
unrestricted        true
$end

$rem_frgm
SCF_CONVERGENCE     5
SCF_ALGORITHM       DIIS_GDM
THRESH              14
$end
```

```Q-Chem
$molecule
read
$end

$rem
jobtype             sp
method              wb97x-v
basis               def2-tzvp
scf_guess           read
mom_method          imom
mom_start           1
sym_ignore          true
symmetry            false
thresh              14
scf_convergence     7
scf_max_cycles      2000
unrestricted        true
make_cube_files     true
plots               1
ovocv_analysis      1
load_ovocv_init_data 1
ovocv_quadrature    9
ovocv_thresh        20000
ovocv_excite_analysis 1
ovocv_excite_type     2
save_ovocv            0
$end

$plots
grid_points 50 50 50
$end
```

--------------------------------

### Cartesian Coordinate Examples

Source: https://manual.q-chem.com/latest/sect_molinput_coords.html

Examples of defining H2O geometry using atomic numbers or atomic symbols.

```text
$molecule
   0 1
   8   0.000000   0.000000  -0.212195
   1   1.370265   0.000000   0.848778
   1  -1.370265   0.000000   0.848778
$end
```

```text
$molecule
   0 1
   O   0.000000   0.000000  -0.212195
   H   1.370265   0.000000   0.848778
   H  -1.370265   0.000000   0.848778
$end
```

--------------------------------

### Q-Chem Input File for Romberg Calculation

Source: https://manual.q-chem.com/latest/sect_Romberg.html

Example input file for ethylene using B3LYP with required high-precision and symmetry settings.

```text
$molecule
0 1
 C        0.00000000   0.00000000 -0.66880000
 H        0.94859916   0.00000000 -1.19917145
 H       -0.94859916   0.00000000 -1.19917145
 C       -0.00000000   0.00000000  0.66880000
 H       -0.54409413   0.77704694  1.19917145
 H        0.54409413  -0.77704694  1.19917145
$end

$rem
   BASIS            =  sto-3g
   EXCHANGE         =  B3lyp
   SCF_CONVERGENCE  =  13  ! tight convergence for finite field calculations
   SCF_MAX_CYCLES   =  200
   CC_PRINT_PREC    =  16  ! decimal points of total energies
   INTEGRAL_SYMMETRY = false ! all symmetries need to be turned off
$end
```

--------------------------------

### Basis Set Projection Input Example

Source: https://manual.q-chem.com/latest/sect_projection.html

Demonstrates using BASIS2 to provide an initial guess for a calculation with a general basis set.

```Q-Chem
$molecule
   0  1
   O
   H  1  r
   H  1  r  2  a

   r    0.9
   a  104.0
$end

$rem
   METHOD        mp2
   BASIS         general
   BASIS2        sto-3g
$end

$basis
   O   0
   S   3   1.000000
           3.22037000E+02   5.92394000E-02
           4.84308000E+01   3.51500000E-01
           1.04206000E+01   7.07658000E-01
   SP  2   1.000000
           7.40294000E+00  -4.04453000E-01   2.44586000E-01
           1.57620000E+00   1.22156000E+00   8.53955000E-01
   SP  1   1.000000
           3.73684000E-01   1.00000000E+00   1.00000000E+00
   SP  1   1.000000
           8.45000000E-02   1.00000000E+00   1.00000000E+00
****
   H   0
   S   2   1.000000
           5.44717800E+00   1.56285000E-01
           8.24547000E-01   9.04691000E-01
   S   1   1.000000
           1.83192000E-01   1.00000000E+00
****
$end
```

--------------------------------

### Generating density and spin-density cube files

Source: https://manual.q-chem.com/latest/sec_cubefiles.html

Example input for generating cube files for ground and excited-state densities, including spin densities, for the HOO radical.

```Q-Chem
$molecule
   0 2
   H     1.004123   -0.180454    0.000000
   O    -0.246002    0.596152    0.000000
   O    -1.312366   -0.230256    0.000000
$end

$rem
   PLOT_SPIN_DENSITY  true
   MAKE_CUBE_FILES    true
   SCF_CONVERGENCE    8
   METHOD             b3lyp
   BASIS              6-31+G*
   CIS_N_ROOTS        1
$end

$plots
grid information and request to plot 2 densities
   20  -5.0  5.0
   20  -5.0  5.0
   20  -5.0  5.0
   0  2  0  0
   0  1
$end
```

--------------------------------

### Example PE-HF calculation input

Source: https://manual.q-chem.com/latest/subsec_PE_job_control.html

Example configuration for a PE-HF calculation involving 4-Nitroaniline and six water molecules.

```text
$comment
The potential file \texttt{gen\_scfman\_pe\_potfile.pot} can be
found in the samples folder.
$end
```

--------------------------------

### Z-matrix Parameterized and Explicit Examples

Source: https://manual.q-chem.com/latest/sect_molinput_coords.html

Examples showing the use of parameters versus explicit values in Z-matrix definitions.

```text
$molecule
   0 1
   O1
   O2  O1  oo
   H1  O1  ho  O2  hoo
   H2  O2  ho  O1  hoo  H1  hooh

   oo   =   1.5
   oh   =   1.0
   hoo  = 120.0
   hooh = 180.0
$end
```

```text
$molecule
   0 1
   O1
   O2  O1  1.5
   H1  O1  1.0  O2  120.0
   H2  O2  1.0  O1  120.0  H1  180.0
$end
```

--------------------------------

### Simulating the IR spectrum of water using QCT-MD

Source: https://manual.q-chem.com/latest/subsec_QCT.html

Example input for a QCT-MD simulation of water, using AIMD_INIT_VELOC set to quasiclassical to trigger quasi-classical initial conditions.

```Q-Chem
$molecule
   0  1
   O     0.000000    0.000000    0.520401
   H    -1.475015    0.000000   -0.557186
   H     1.475015    0.000000   -0.557186
$end

$rem
   JOBTYPE                     freq
   INPUT_BOHR                  true
   METHOD                      hf
   BASIS                       3-21g
$end

@@@

$molecule
  read
$end

$rem
   JOBTYPE                     aimd
   INPUT_BOHR                  true
   METHOD                      hf
   BASIS                       3-21g
   SCF_CONVERGENCE             6
   TIME_STEP                   20    !  (in atomic units)
   AIMD_STEPS                  1250  !  600 fs total simulation time
   AIMD_TEMP                   12
   AIMD_PRINT                  2
   FOCK_EXTRAP_ORDER           6     ! Use a 6th-order extrapolation
   FOCK_EXTRAP_POINTS          12    ! of the previous 12 Fock matrices
   AIMD_MOMENTS                1
   AIMD_NUCL_SAMPLE_RATE       5
   AIMD_NUCL_VACF_POINTS       1000
   AIMD_INIT_VELOC             quasiclassical
   AIMD_QCT_WHICH_TRAJECTORY   1     ! Loop over several values to get
                                     ! the correct Boltzmann distribution.
$end
```

--------------------------------

### Q-Chem Input for ωB97M-V/SNK Energy Calculation

Source: https://manual.q-chem.com/latest/sect_snk.html

Example input file demonstrating the configuration of SNK parameters alongside standard job settings.

```text
$molecule
0 1
O 0.0000000000  0.0000000000  0.21981483259
H 0.0000000000  1.4194772274 -0.87926122007
H 0.0000000000 -1.4194772274 -0.87926122007
$end

$rem
input_bohr = true
jobtype = sp
method = wB97M-V
basis = cc-pvtz
scf_convergence = 8

snk 1
snk_batch_size 256
snk_thresh_b 12
snk_thresh_e 10
snk_thresh_k 7
snk_thresh_fp32_m 5

$end
```
Tokens:
Raw