User Manual¶

QUICK uses a simple text based input file that consists of a line with keywords followed by an empty line, the molecular coordinates in xyz format, and potentially point charge information after another empty line. Please see the Hands-on Tutorials for details on the input file format.

Units¶

The QUICK input file requires atomic coordinates in Angstrom and charges (molecular charge and point charges) in atomic units.

The QUICK output reports coordinates in Angstroms, and charges, energies, and gradients in atomic units. This means that energies are reported in Hartree and gradients in Hartree/Bohr.

Keywords for QUICK Input¶

1. Hamiltonians¶

HF : Hartree-Fock Hamiltonian to be used

DFT : Density Functional Theory to be used.

NOTE 1 : One Hamiltonian must be selected. There is no default.

2. Density Functional Theory¶

QUICK has two built-in DFT methods that do not rely on Libxc:

BLYP : Built in BLYP functional (A. D. Becke, Phys. Rev. A 38, 3098 (1988), C. Lee, W. Yang, and R. G. Parr, Phys. Rev. B 37, 785 (1988), B. Miehlich, A. Savin, H. Stoll, and H. Preuss, Chem. Phys. Lett. 157, 200 (1989))

B3LYP: Built in B3LYP functional (P. J. Stephens, F. J. Devlin, C. F. Chabalowski, and M. J. Frisch, J. Phys. Chem. 98, 11623 (1994) )

Following functionals use Libxc (version 4.0.4) and can be requested by their popular names:

BP86: BP86 functional (A. D. Becke, Phys. Rev. A 38, 3098 (1988), J. P. Perdew, Phys. Rev. B 33, 8822 (1986))

B97: B97 functional (A. D. Becke, J. Chem. Phys. 107, 8554 (1997))

B97-GGA1: B97-GGA1 functional (A. J. Cohen and N. C. Handy, Chem. Phys. Lett. 316, 160 (2000))

PW91: PW91 functional (J. P. Perdew, J. A. Chevary, S. H. Vosko, K. A. Jackson, M. R. Pederson, D. J. Singh, and C. Fiolhais, Phys. Rev. B 46, 6671 (1992))

OLYP: OLYP functional (N. C. Handy and A. J. Cohen, Mol. Phys. 99, 403 (2001), C. Lee, W. Yang, and R. G. Parr, Phys. Rev. B 37, 785 (1988))

O3LYP: O3LYP functional (A. J. Cohen and N. C. Handy, Mol. Phys. 99, 607 (2001))

PBE: PBE functional (J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996), J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 78, 1396 (1997))

REVPBE: Revised PBE functional (Y. Zhang and W. Yang, Phys. Rev. Lett. 80, 890 (1998), J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996), J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 78, 1396 (1997))

PBE0: PBE0/PBEH functional (C. Adamo and V. Barone, J. Chem. Phys. 110, 6158 (1999), M. Ernzerhof and G. E. Scuseria, J. Chem. Phys. 110, 5029 (1999))

Except for the built-in BLYP and B3LYP functionals QUICK makes use of the Libxc density functional library (version 4.0.4). All LDA, GGA and hybrid-GGA functionals available in Libxc can be requested. As a reminder, (hybrid) meta-GGA and range-separated hybrid functionals are not supported at present. You must make sure to select a valid combination of exchange and correlation functionals. A generic Libxc functional can be requested as follows:

LIBXC=FUNCTIONAL1,FUNCTIONAL2 : Where FUNCTIONAL1 and FUNCTIONAL2 are exchange and correlation functionals. Note: Spaces near ‘=’ or ‘,’ are not allowed.

See here for a list of available functionals in the current QUICK version.

If you are using Libxc in your work, please cite following paper:

Susi Lehtola, Conrad Steigemann, Micael J.T. Oliveira, and Miguel A.L. Marques, Recent developments in Libxc - A comprehensive library of functionals for density functional theory, Software X 7, 1 (2018).

Grimme type dispersion corrections are requested by adding one of the following keywords:

D2 : use Grimme’s D2 dispersion correction in DFT.

D3 : use Grimme’s D3 dispersion correction with zero damping.

D3BJ : use Grimme’s D3 dispersion correction with Becke-Johnson damping.

D3M : use Grimme’s D3 dispersion correction with modified zero damping by Sherrill and coworkers.

D3MBJ - use Grimme’s D3 dispersion correction with modified Becke-Johnson damping by Sherrill and coworkers.

XCCUTOFF=Float: user defined threshold for grid pruning in exchange correlation algorithm. Default: 1.0E-7

3. Basis sets¶

BASIS=BASIS_SET_NAME : Selects BASIS_SET_NAME basis set for the calculation. BASIS_SET_NAME could be any of the following. The basis set name is not case sensitive.

STO-3G
3-21G
6-31G
6-31G* or 6-31G(d)
6-31G** or 6-31G(d,p)
6-311G
6-311G* or 6-311G(d)
6-311G** or 6-311G(d,p)
6-31+G* or 6-31+G(d)
6-31+G** or 6-31+G(d,p)
6-31++G** or 6-31++G(d,p)
6-311+G(2d,p)
6-311++G(2d,2p)
cc-pVDZ
def2-SV(P)
def2-SVP
def2-SVPD
PC-0
PC-1

Note 1: We follow the same basis set names reported at the basis set exchange web page.

Note 2: The current version of the QUICK ERI engine only support basis functions up to d. Therefore, energy and gradient calculations with functions up to d are possible.

Note 3: ECPs are currently not supported by QUICK. Due to this reason, we have excluded elements that require ECPs from the above basis sets that are included with QUICK.

4. SCF Convergence¶

SCF=Integer : user defined maximum self-consistent field cycles = Integer. Default: 200

NCYC=Integer : user defined self-consistent field cycles to turn on incremental Fock build = Integer. Default: 3

DENSERMS=Float : user defined density matrix maximum RMS for convergence. Default : 1.0E-6.

CUTOFF=Float : user defined integral cutoff. Default : 1.0E-8.

BASISCUTOFF=Float : user defined cutoff for neglecting insignificant basis functions. Default : 1.0E-6.

COARSEINT : use coarse cutoffs. (i.e. DENSERMS=1.0E-5, CUTOFF=1.0E-6, BASISCUTOFF=1.0E-5, XCCUTOFF=1.0E-6)

TIGHTINT : use tight cutoffs. (i.e. DENSERMS=1.0E-7, CUTOFF=1.0E-8, BASISCUTOFF=1.0E-7, XCCUTOFF=1.0E-8)

5. Atomic Charges¶

CHARGE=Integer : A net charge is to be placed on system. Default: 0

EXTCHARGES : External charges are included in the system. The point charges must be listed after the molecular Cartesian coordinates in the input file. See the corresponding section in the Hands-on Tutorials of this manual.

DIPOLE : Write dipole moments, Mulliken and Löwdin charges into the output file.

6. Gradient Calculation¶

GRADIENT : Calculates analytical gradients.

GRADCUTOFF=Float : user defined cutoff for gradients. Default : 1.0E-7 (automatically set to 1.0E-6 or 1.0E-8 if COARSEINT or TIGHTINT keyword is specified)

7. Geometry Optimization¶

OPTIMIZE=Integer : Performs a geometry optimization with a maximum of Integer steps. Default: 3 x Number of atoms.

DLFIND : Use DL-FIND optimizer. This is the default.

LOPT : Use legacy QUICK optimizer instead of DL-FIND.

GTOL : User defined maximum RMS value of the gradient vector. Default: 4.5E-4

ETOL : User defined maximum energy change between two consecutive optimization cycles. Default: 1.0E-6

ICOORD=Integer : User defined coordinate system for DL-Find geometry optimization. Default: 3 (delocalized internal coordinates(DLC)). Other available option is 0 (Cartesian).

ALLOW_BAD_SCF : Allow unconverged SCF in geometry optimization. By default, the optimization will not proceed if the SCF fails to converge.

If you are using the DL-FIND optimizer in your work, please make sure to cite the following paper:

Johannes Kästner, Joanne M. Carr, Thomas W. Keal, Walter Thiel, Adrian Wander, and Paul Sherwood, DL-FIND: An Open-Source Geometry Optimizer for Atomistic Simulations, J. Phys. Chem. A, 2009, 113 (43), 11856-11865..

8. Data Exporting¶

EXPORT=MOLDEN : Generates a molden file that contains orbitals, charges, geometries, etc.

Last updated by Andy Goetz on 02/17/2023.