# Parameters for calculating vdwForce

Parameters here are for calculating the van der Waals force.

## calculation.vdwForce.method

keyword: calculation.vdwForce.method

possible values: ‘Grimme’

default value: ‘Grimme’

description: The method being used for the calculation.

an example:

```calculation.vdwForce.method = 'Grimme'
```

## calculation.vdwForce.Grimme.s6

keyword: calculation.vdwForce.Grimme.s6

possible values: a double number

default value: depends on the the DF used

description: The global scaling factor which depends on the DF used.

an example:

```calculation.vdwForce.Grimme.s6 = 0.75
```

## calculation.vdwForce.Grimme.d

keyword: calculation.vdwForce.Grimme.d

possible values: a double number

default value: 20

description: The damping parameter used in the damping function: the larger the d, the sharp the damping function which goes from zero to one with increasing atomic distance.

an example:

```calculation.vdwForce.Grimme.d = 25
```

## calculation.vdwForce.Grimme.dcut

keyword: calculation.vdwForce.Grimme.dcut

possible values: a double number with proper length unit such as ‘au’, ‘a.u.’, ‘atomic unit’, ‘Bohr’ ‘an’, ‘ang’, ‘angstrom’, ‘nm’, ‘nanometer’, where ‘au’ ‘a.u.’, and ‘atomic unit’ are for Bohr, ‘an’ and ‘ang’ for angstrom, and ‘nm’ for nanometer.

default value: 30 angstrom

description: The maximun of the interaction distance.

an example:

```calculation.vdwForce.Grimme.dcut = 25 angstrom
```

## calculation.vdwForce.Grimme.C6R0

keyword: calculation.vdwForce.Grimme.C6R0

possible values: n*3 double array

default value: []

description: The parameter is used with the Grimme mathod for an user to define or update the C6 and R0 values for some elements being considered, where each row is composed of [Z, C6, R0] and Z is the atomic number of the element, C6 is the atomic vdw energy in unit of J*nm^6/mol, and R0 is the atomic vdw radii in unit of angstrom.

an example:

```calculation.vdwForce.Grimme.C6R0 = [86 70.0 2.1]
```

## calculation.hessian.dynamicalMatrix

keyword: calculation.hessian.dynamicalMatrix

possible values: true or false

default value: true

description: If true, the dynamical matrix will be calculated.

an example:

```calculation.hessian.dynamicalMatrix = true
```

## calculation.hessian.hamiltonianDerivative

keyword: calculation.hessian.hamiltonianDerivative

possible values: true or false

default value: true

description: If true, the derivative of the hamiltonian matrix will be calculated, which will be used in the calculation of electron-phonon coupling.

an example:

```calculation.hessian.hamiltonianDerivative = true
```