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# OPTKING

Performs geometry optimizations and vibrational frequency analyses.

## Optimization Algorithm

### CONSECUTIVE_BACKSTEPS

> Set number of consecutive backward steps allowed in optimization

> - Type: integer
> - Default: 0

### FIXED_BEND

> Specify angles between atoms to be fixed (eq. value specified)

> - Type: string
> - Default: No Default

### FIXED_DIHEDRAL

> Specify dihedral angles between atoms to be fixed (eq. value specified)

> - Type: string
> - Default: No Default

### FIXED_DISTANCE

> Specify distances between atoms to be fixed (eq. value specified)

> - Type: string
> - Default: No Default

### FROZEN_BEND

> Specify angles between atoms to be frozen (unchanged)

> - Type: string
> - Default: No Default

### FROZEN_DIHEDRAL

> Specify dihedral angles between atoms to be frozen (unchanged)

> - Type: string
> - Default: No Default

### FROZEN_DISTANCE

> Specify distances between atoms to be frozen (unchanged)

> - Type: string
> - Default: No Default

### GEOM_MAXITER

> Maximum number of geometry optimization steps

> - Type: integer
> - Default: 50

### INTERFRAG_STEP_LIMIT

> Maximum step size in bohr or radian along an interfragment coordinate

> - Type: double
> - Default: 0.4

### INTRAFRAG_STEP_LIMIT

> Initial maximum step size in bohr or radian along an internal coordinate

> - Type: double
> - Default: 0.4

### INTRAFRAG_STEP_LIMIT_MAX

> Upper bound for dynamic trust radius [au]

> - Type: double
> - Default: 1.0

### INTRAFRAG_STEP_LIMIT_MIN

> Lower bound for dynamic trust radius [au]

> - Type: double
> - Default: 0.001

### IRC_DIRECTION

> IRC mapping direction

> - Type: string
> - Possible Values: FORWARD, BACKWARD
> - Default: FORWARD

### IRC_STEP_SIZE

> IRC step size in bohr(amu).

> - Type: double
> - Default: 0.2

### IRC_STOP

> Decide when to stop IRC calculations

> - Type: string
> - Possible Values: ASK, STOP, GO
> - Default: STOP

### OPT_TYPE

> Specifies minimum search, transition-state search, or IRC following

> - Type: string
> - Possible Values: MIN, TS, IRC
> - Default: MIN

### RFO_FOLLOW_ROOT

> Do follow the initial RFO vector after the first step?

> - Type: boolean
> - Default: false

### RFO_ROOT

> Root for RFO to follow, 0 being lowest (for a minimum)

> - Type: integer
> - Default: 0

### STEP_TYPE

> Geometry optimization step type, either Newton-Raphson or Rational Function Optimization

> - Type: string
> - Possible Values: RFO, NR, SD, LINESEARCH_STATIC
> - Default: RFO

## Convergence Control

### FLEXIBLE_G_CONVERGENCE

> Even if a user-defined threshold is set, allow for normal, flexible convergence criteria

> - Type: boolean
> - Default: false

### G_CONVERGENCE

> Set of optimization criteria. Specification of any MAX_*_G_CONVERGENCE or RMS_*_G_CONVERGENCE options will append to overwrite the criteria set here unless FLEXIBLE_G_CONVERGENCE is also on. See Table Geometry Convergence for details.

> - Type: string
> - Possible Values: QCHEM, MOLPRO, GAU, GAU_LOOSE, GAU_TIGHT, GAU_VERYTIGHT, TURBOMOLE, CFOUR, NWCHEM_LOOSE
> - Default: QCHEM

### MAX_DISP_G_CONVERGENCE

> Convergence criterion for geometry optmization: maximum displacement (internal coordinates, atomic units).

> - Type: conv double
> - Default: 1.2e-3

### MAX_ENERGY_G_CONVERGENCE

> Convergence criterion for geometry optmization: maximum energy change.

> - Type: conv double
> - Default: 1.0e-6

### MAX_FORCE_G_CONVERGENCE

> Convergence criterion for geometry optmization: maximum force (internal coordinates, atomic units).

> - Type: conv double
> - Default: 3.0e-4

### RMS_DISP_G_CONVERGENCE

> Convergence criterion for geometry optmization: rms displacement (internal coordinates, atomic units).

> - Type: conv double
> - Default: 1.2e-3

### RMS_FORCE_G_CONVERGENCE

> Convergence criterion for geometry optmization: rms force (internal coordinates, atomic units).

> - Type: conv double
> - Default: 3.0e-4

## Hessian Update

### CART_HESS_READ

> Do read Cartesian Hessian? Only for experts - use FULL_HESS_EVERY instead.

> - Type: boolean
> - Default: false

### FULL_HESS_EVERY

> Frequency with which to compute the full Hessian in the course of a geometry optimization. 0 means to compute the initial Hessian only, 1 means recompute every step, and N means recompute every N steps. The default (-1) is to never compute the full Hessian.

> - Type: integer
> - Default: -1

### HESS_UPDATE

> Hessian update scheme

> - Type: string
> - Possible Values: NONE, BFGS, MS, POWELL, BOFILL
> - Default: BFGS

### HESS_UPDATE_LIMIT

> Do limit the magnitude of changes caused by the Hessian update?

> - Type: boolean
> - Default: true

### HESS_UPDATE_LIMIT_MAX

> If HESS_UPDATE_LIMIT is true, changes to the Hessian from the update are limited to the larger of HESS_UPDATE_LIMIT_SCALE * (the previous value) and HESS_UPDATE_LIMIT_MAX [au].

> - Type: double
> - Default: 1.00

### HESS_UPDATE_LIMIT_SCALE

> If HESS_UPDATE_LIMIT is true, changes to the Hessian from the update are limited to the larger of HESS_UPDATE_LIMIT_SCALE * (the previous value) and HESS_UPDATE_LIMIT_MAX [au].

> - Type: double
> - Default: 0.50

### HESS_UPDATE_USE_LAST

> Number of previous steps to use in Hessian update, 0 uses all

> - Type: integer
> - Default: 1

### INTRAFRAG_HESS

> Model Hessian to guess intrafragment force constants

> - Type: string
> - Possible Values: FISCHER, SCHLEGEL, SIMPLE, LINDH
> - Default: SCHLEGEL

## Fragment/Internal Coordinate Control

### ADD_AUXILIARY_BONDS

> Do add bond coordinates at nearby atoms for non-bonded systems?

> - Type: boolean
> - Default: false

### COVALENT_CONNECT

> When determining connectivity, a bond is assigned if interatomic distance is less than (this number) * sum of covalent radii.

> - Type: double
> - Default: 1.3

### FRAG_MODE

> For multi-fragment molecules, treat as single bonded molecule or via interfragment coordinates. A primary difference is that in `MULTI` mode, the interfragment coordinates are not redundant.

> - Type: string
> - Possible Values: SINGLE, MULTI
> - Default: SINGLE

### FREEZE_INTERFRAG

> Do freeze all interfragment modes?

> - Type: boolean
> - Default: false

### FREEZE_INTRAFRAG

> Do freeze all fragments rigid?

> - Type: boolean
> - Default: false

### H_BOND_CONNECT

> For now, this is a general maximum distance for the definition of H-bonds

> - Type: double
> - Default: 4.3

### INTCOS_GENERATE_EXIT

> Do only generate the internal coordinates and then stop?

> - Type: boolean
> - Default: false

### INTERFRAGMENT_CONNECT

> When connecting disparate fragments when frag_mode = SIMPLE, a “bond” is assigned if interatomic distance is less than (this number) * sum of covalent radii. The value is then increased until all the fragments are connected (directly or indirectly).

> - Type: double
> - Default: 1.8

### INTERFRAG_DIST_INV

> Do use for the stretching coordinate between fragments? Otherwise, use .

> - Type: boolean
> - Default: false

### INTERFRAG_HESS

> Model Hessian to guess interfragment force constants

> - Type: string
> - Possible Values: DEFAULT, FISCHER_LIKE
> - Default: DEFAULT

### INTERFRAG_MODE

> When interfragment coordinates are present, use as reference points either principal axes or fixed linear combinations of atoms.

> - Type: string
> - Possible Values: FIXED, INTERFRAGMENT
> - Default: FIXED

## Misc.

### FINAL_GEOM_WRITE

> Do save and print the geometry from the last projected step at the end of a geometry optimization? Otherwise (and by default), save and print the previous geometry at which was computed the gradient that satisfied the convergence criteria.

> - Type: boolean
> - Default: false

### KEEP_INTCOS

> Keep internal coordinate definition file.

> - Type: boolean
> - Default: false

### LINESEARCH_STATIC_MAX

> If doing a static line search, this fixes the largest step, whose largest change in an internal coordinate is set to this value (in au)

> - Type: double
> - Default: 0.100

### LINESEARCH_STATIC_MIN

> If doing a static line search, this fixes the shortest step, whose largest change in an internal coordinate is set to this value (in au)

> - Type: double
> - Default: 0.001

### LINESEARCH_STATIC_N

> If doing a static line search, scan this many points.

> - Type: integer
> - Default: 8

### TEST_B

> Do test B matrix?

> - Type: boolean
> - Default: false

### TEST_DERIVATIVE_B

> Do test derivative B matrix?

> - Type: boolean
> - Default: false

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