# 13.4.4 Job Control for the NEO-SCF methods

The NEO method is a natural extension of the Self-Consistent-Field methods and it inherits most of its functionalities. Thus, the keywords that are used in the SCF Job Control are used in the NEO-SCF methods with a few additional keywords. The NEO-SCF methods require definition of the nuclear basis sets (see Examples for more information). Refer to Ref. Culpitt:2019 for selection of the protonic basis sets. Only pure (Spherical) Gaussian basis sets are currently available. The following three $rem variables must be specified in order to run NEO-SCF calculations: NEO Enable a NEO-SCF calculation. TYPE: BOOLEAN DEFAULT: FALSE OPTIONS: TRUE Enable a NEO-SCF calculation. FALSE Disable a NEO-SCF calculation. RECOMMENDATION: Set to TRUE if desired. METHOD Specifies the exchange-correlation functional. TYPE: STRING DEFAULT: No default OPTIONS: NAME Use METHOD = NAME, where NAME is one of the following: HF for Hartree-Fock theory; one of the DFT methods listed in Section 5.3.4.; RECOMMENDATION: In general, consult the literature to guide your selection. Our recommendations for DFT are indicated in bold in Section 5.3.4. BASIS Specifies the electronic basis sets to be used. TYPE: STRING DEFAULT: No default basis set OPTIONS: General, Gen User defined ($basis keyword required). Symbol Use standard basis sets as per Chapter 8. Mixed Use a mixture of basis sets (see Chapter 8).
RECOMMENDATION:
Consult literature and reviews to aid your selection.

In addition, the following $rem variables, that appear in the conventional SCF calculations can be used to customize the NEO-SCF calculation: SCF_CONVERGENCE NEO-SCF is considered converged when the electronic wave function error is less that $10^{-\mathrm{SCF\_CONVERGENCE}}$. Adjust the value of THRESH at the same time. (Starting with Q-Chem 3.0, the DIIS error is measured by the maximum error rather than the RMS error as in earlier versions.) TYPE: INTEGER DEFAULT: 5 For single point energy calculations. 8 For geometry optimizations. OPTIONS: User-defined RECOMMENDATION: None. NEO_N_SCF_CONVERGENCE NEO-SCF is considered converged when the nuclear wave function error is less that $10^{-\mathrm{NEO\_N\_SCF\_CONVERGENCE}}$. TYPE: INTEGER DEFAULT: 7 OPTIONS: User-defined RECOMMENDATION: None. UNRESTRICTED Controls the use of restricted or unrestricted orbitals. TYPE: LOGICAL DEFAULT: FALSE Closed-shell systems. TRUE Open-shell systems. OPTIONS: FALSE Constrain the spatial part of the alpha and beta orbitals to be the same. TRUE Do not Constrain the spatial part of the alpha and beta orbitals. RECOMMENDATION: The ROHF method is not available. Note that for unrestricted calculations on systems with an even number of electrons it is usually necessary to break $\alpha$/$\beta$ symmetry in the initial guess, by using SCF_GUESS_MIX or providing$occupied information (see Section 4.4 on initial guesses).

MAX_SCF_CYCLES
Controls the maximum number of SCF iterations permitted.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
$n$ $n>0$ User-selected.
RECOMMENDATION:
Increase for slowly converging systems such as those containing transition metals.

SCF_ALGORITHM
Algorithm used for converging the SCF.
TYPE:
STRING
DEFAULT:
DIIS Pulay DIIS.
OPTIONS:
DIIS Pulay DIIS. DM Direct minimizer. DIIS_DM Uses DIIS initially, switching to direct minimizer for later iterations (See THRESH_DIIS_SWITCH, MAX_DIIS_CYCLES). DIIS_GDM Use DIIS and then later switch to geometric direct minimization (See THRESH_DIIS_SWITCH, MAX_DIIS_CYCLES). GDM Geometric Direct Minimization. RCA Relaxed constraint algorithm RCA_DIIS Use RCA initially, switching to DIIS for later iterations (see THRESH_RCA_SWITCH and MAX_RCA_CYCLES described later in this chapter) ROOTHAAN Roothaan repeated diagonalization.
RECOMMENDATION:
In the NEO methods, the GDM procedure is recommended.

JOBTYPE
Specifies the calculation.
TYPE:
STRING
DEFAULT:
Default is single-point, which should be changed to one of the following options.
OPTIONS:
OPT Equilibrium structure optimization. TS Transition structure optimization is currently not available in NEO. RPATH Intrinsic reaction path following is currently not available in NEO.
RECOMMENDATION:
Application-dependent. Always use SYM_IGNORE = 1 with geometry optimization.

XC_GRID
Specifies the type of grid to use for DFT calculations.
TYPE:
INTEGER
DEFAULT:
Functional-dependent; see Table 5.3.
OPTIONS:
0 Use SG-0 for H, C, N, and O; SG-1 for all other atoms. $n$ Use SG-$n$ for all atoms, $n=1,2$, or 3 $XY$ A string of two six-digit integers $X$ and $Y$, where $X$ is the number of radial points and $Y$ is the number of angular points where possible numbers of Lebedev angular points, which must be an allowed value from Table 5.2 in Section 5.5. $-XY$ Similar format for Gauss-Legendre grids, with the six-digit integer $X$ corresponding to the number of radial points and the six-digit integer $Y$ providing the number of Gauss-Legendre angular points, $Y=2N^{2}$.
RECOMMENDATION:
Use the default unless numerical integration problems arise. Larger grids may be required for optimization and frequency calculations.

Additional NEO specific $rem variables can be used to customize the NEO-SCF calculation: NEO_E_CONV Energy convergence criteria in the NEO-SCF calculations so that the difference in energy between electronic and protonic iterations is less than $10^{-\mathrm{NEO\_E\_CONV}}$. TYPE: INTEGER DEFAULT: 8 OPTIONS: User-defined RECOMMENDATION: Tighter criteria for geometry optimization are recommended. NEO_BASIS_LIN_DEP_THRESH This keyword is used to set the liner dependency threshold for nuclear basis sets. It is defined as $10^{-\mathrm{NEO\_BASIS\_LIN\_DEP\_THRESH}}$. TYPE: DOUBLE DEFAULT: 5.0 OPTIONS: User-defined RECOMMENDATION: No recommendation. NEO_PURECART This keyword is used to specify Cartesian or spherical Gaussians for nuclear basis functions. TYPE: INTEGER DEFAULT: 2222 OPTIONS: User-defined RECOMMENDATION: Default are Cartesian Gaussians. 1111 would define spherical Gaussians similar to keyword PURECART. Current NEO calculations do not support Cartesian electronic or nuclear basis sets with h angular momentum. NEO_ISOTOPE Enable calculations of different types of isotopes. Only one type of isotope is allowed at present. TYPE: INTEGER DEFAULT: 1 Default is the proton isotope. OPTIONS: 1 This NEO calculation is using proton isotope. 2 This NEO calculation is using deuterium isotope. 3 This NEO calculation is using tritium isotope. RECOMMENDATION: Refer to the NEO literature for the best performance on the isotope effects calculations. NEO_VPP Remove $J-K$ terms from the nuclear Fock matrix and the corresponding kernel terms for NEO excited state methods for the case of one quantum proton. TYPE: INTEGER DEFAULT: 0 OPTIONS: 1 Enable this option. 0 Disable this option. RECOMMENDATION: Use this only in the case of one quantum hydrogen. NEO_EPC Specifies the electron-proton correlation functional. TYPE: STRING DEFAULT: No default OPTIONS: NAME Use NEO_EPC = NAME, where NAME can be either epc172 or epc19. RECOMMENDATION: Consult the NEO literature to guide your selection. The following additional$rem variables can be used to customize the NEO excited states methods calculation to obtain excitation energies:

SET_ROOTS
Sets the number of NEO excited state roots to find by Davidson or display the number of roots obtained by direct diagonalization.
TYPE:
INTEGER
DEFAULT:
0 Do not look for any excited states.
OPTIONS:
$n$ $n>0$ Looks for $n$ NEO excited states.
RECOMMENDATION:
None

SET_RPA
Do a NEO-TDDFT or NEO-TDHF calculation.
TYPE:
LOGICAL/INTEGER
DEFAULT:
FALSE
OPTIONS:
FALSE Do a NEO-TDA or NEO-CIS calculation. TRUE Do a NEO-TDDFT or NEO-TDHF calculation.
RECOMMENDATION:
Consult the NEO literature to guide your selection.

DIRECT_DIAG
Perform direct diagonalization to obtain all the NEO excitation energies.
TYPE:
INTEGER
DEFAULT:
0 Use Davidson algorithm.
OPTIONS:
1 Do the direct diagonalization. 0 Use Davidson algorithm.
RECOMMENDATION:
Only use this option when Davidson solutions are not stable.