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# 12.16.2 Job Control

(February 4, 2022)

A MBE($n$) calculation is requested by setting MANY_BODY_INT = TRUE in the $rem section. The level of theory used for the fragments will be whatever is specified in the$rem section. Researchers who use Q-Chem’s MBE code are asked to cite Ref. 969, 637. In addition, please cite Ref. 967 for the MBCP($n$) method.

A MBE($n$) calculation is requested by setting MANY_BODY_INT = TRUE in the $rem section. The level of theory used for the fragments will be whatever is specified in the$rem section. Researchers who use Q-Chem’s MBE code are asked to cite Ref. 969, 637. In addition, please cite Ref. 967 for the MBCP($n$) method.

MANY_BODY_INT

MANY_BODY_INT
Perform a MBE calculation.
TYPE:
BOOLEAN
DEFAULT:
FALSE
OPTIONS:
TRUE Perform a MBE calculation. FALSE Do not perform a MBE calculation.
RECOMMENDATION:
NONE

Additional MBE-specific options, such as the order of the expansion ($n$), are specified in a $mbe input section, as described below. Order Specifies the order of the many-body expansion. INPUT SECTION:$mbe
TYPE:
INTEGER
DEFAULT:
None
OPTIONS:
$n$ Perform an MBE($n$) calculation.
RECOMMENDATION:
Orders $n\leq 5$ are available.

Embed
Specifies the embedding method for EE-MBE($n$).
INPUT SECTION: $mbe TYPE: STRING DEFAULT: None OPTIONS: None Do not use embedding. Charges Use atomic point charges. Density Full Coulomb embedding using monomer densities. RECOMMENDATION: Use of atomic point charges requires a$mbe_charges section to specify the charges.

Q-Chem’s implementation of EE-MBE($n$) with atomic point charges is designed to use with a $mbe_charges input section to specify fixed embedding charges. (Use of these charges is intended to accelerate convergence of the MBE by capturing many-body polarization effects and thus making the higher-order $n$-body terms smaller, although three- and four-body terms remain non-negligible even with embedding charges.637, 706) The format of the$mbe_charges section is simply a list of charges in the same order as the atoms in the $molecule section. An example is provided below. Many-body counterpoise corrections are requested with two keywords in the$mbe input section: BSSE_Type and BSSE_Order. These have only been implemented up to $n=3$, as the $n=2$ terms make by far the most significant contribution.706

BSSE_Order
Perform a many-body counterpoise correction of the MBCP($n$) or VMFC($n$) variety.
INPUT SECTION: $mbe TYPE: INTEGER DEFAULT: 0 OPTIONS: 0 Do not perform a counterpoise correction. $n$ Perform a counterpoise correction truncated at order $n$. RECOMMENDATION: Orders $n\leq 3$ are available. Use the keyword BSSE_Type to choose between MBCP and VMFC. BSSE_Type Select the type of many-body counterpoise correction, MBCP($n)$ or VMFC($n$). INPUT SECTION:$mbe
TYPE:
STRING
DEFAULT:
MBCP
OPTIONS:
MBCP Use MBCP($n$). VMFC Use VMFC($n$).
RECOMMENDATION:
The two methods are equivalent for $n=2$ but different for $n\geq 3$. MBCP($n$) contains fewer terms but generally provides comparable results as compared to the formally more complete VMFC($n$) approach.

Example 12.40  Example showing a EE-MBE(3) calculation using TIP3P charges.

$molecule 0 1 -- 0 1 O -1.126149 -1.748387 -0.423240 H -0.234788 -1.493897 -0.661862 H -1.062789 -2.681331 -0.218819 -- 0 1 O -0.254210 1.611495 -1.293845 H -1.001520 1.163510 -1.690129 H -0.153399 2.411746 -1.809248 -- 0 1 O 1.694541 -0.226287 1.705739 H 0.785920 0.073487 1.677909 H 2.047134 0.150917 2.511706 -- 0 1 O -0.864533 0.522472 1.218817 H -0.694120 1.093542 0.469789 H -1.131418 -0.310426 0.829702$end

$rem SYM_IGNORE true METHOD B3LYP BASIS cc-pVDZ MANY_BODY_INT true THRESH 14 SCF_CONVERGENCE 7$end

$mbe order 3 embed charges$end

$mbe_charges -0.834 0.417 0.417 -0.834 0.417 0.417 -0.834 0.417 0.417 -0.834 0.417 0.417$end


View output

Example 12.41  Example of a MBCP(3) calculation.

$molecule 0 1 -- 0 1 O -1.126149 -1.748387 -0.423240 H -0.234788 -1.493897 -0.661862 H -1.062789 -2.681331 -0.218819 -- 0 1 O -0.254210 1.611495 -1.293845 H -1.001520 1.163510 -1.690129 H -0.153399 2.411746 -1.809248 -- 0 1 O 1.694541 -0.226287 1.705739 H 0.785920 0.073487 1.677909 H 2.047134 0.150917 2.511706 -- 0 1 O -0.864533 0.522472 1.218817 H -0.694120 1.093542 0.469789 H -1.131418 -0.310426 0.829702$end

$rem MANY_BODY_INT TRUE METHOD B3LYP BASIS cc-pVDZ THRESH 12 SCF_CONVERGENCE 6$end

$mbe BSSE_Order 3 BSSE_Type MBCP ! this is the default$end


View output