Dear all,

I have a concern and a question about angle_style class2.

One doc page (http://lammps.sandia.gov/doc/angle_class2.html), it gives the examples

angle_style class2

angle_coeff * 75.0

angle_coeff 1 bb 10.5872 1.0119 1.5228

angle_coeff * ba 3.6551 24.895 1.0119 1.5228

But in the description, it says

“Coefficients for the Ea, Ebb, and Eba formulas must be defined for each angle type via the bond_coeff command as in the example above …”

Because bond_style class2 (http://lammps.sandia.gov/doc/bond_class2.html) and bond_coeff have the different format than angle_style class2. Shouldn’t it be "Coefficients for … via the ‘angle_style’ command …” on doc page?

The other question is also on angle_class2 page, it says

For the Ebb formula, each line in a bond_coeff (I assume this should be angle_coeff) command in the input script lists 4 coefficients, the first of which is “bb” to indicate they are BondBond coefficients. In a data file, these coefficients should be listed under a “BondBond Coeffs” heading and you must leave out the “bb”, i.e. only list 3 coefficients after the angle type.

Based on the above statement, are the following set-up identical?

angle_coeff 1 bb 10.5872 1.0119 1.5228

BondBond Coeffs 1 10.5872 1.0119 1.5228

If the answer is yes, does it mean we only use either angle_coeff 1 bb 10.5872 1.0119 1.5228 for .in file or BondBond Coeffs 1 10.5872 1.0119 1.5228 for .data file?

Appreciate your help.

Cheers,

F.S.

Dear all,

I have a concern and a question about angle_style class2.

One doc page (LAMMPS Molecular Dynamics Simulator), it gives the

examples

angle_style class2

angle_coeff * 75.0

angle_coeff 1 bb 10.5872 1.0119 1.5228

angle_coeff * ba 3.6551 24.895 1.0119 1.5228

But in the description, it says

"Coefficients for the Ea, Ebb, and Eba formulas must be defined for each

angle type via the bond_coeff command as in the example above …"

Because bond_style class2 (LAMMPS Molecular Dynamics Simulator)

and bond_coeff have the different format than angle_style class2. Shouldn’t

it be "Coefficients for … via the ‘angle_style' command …” on doc page?

not angle style, but angle_coeff, but otherwise yes. the class2 docs

suffer a little bit from copy-n-modify bugs.

The other question is also on angle_class2 page, it says

For the Ebb formula, each line in a bond_coeff (I assume this should be

angle_coeff) command in the input script lists 4 coefficients, the first of

which is "bb" to indicate they are BondBond coefficients. In a data file,

these coefficients should be listed under a "BondBond Coeffs" heading and

you must leave out the "bb", i.e. only list 3 coefficients after the angle

type.

Based on the above statement, are the following set-up identical?

angle_coeff 1 bb 10.5872 1.0119 1.5228

BondBond Coeffs 1 10.5872 1.0119 1.5228

yes.

If the answer is yes, does it mean we only use either angle_coeff 1 bb

10.5872 1.0119 1.5228 for .in file or BondBond Coeffs 1 10.5872 1.0119

1.5228 for .data file?

you can use both. whatever comes later will override the previous settings.

axel.

Thanks Dr. Axel.

Since talking about class2, I have another concern.

In order to consider one-center angle-angle interaction term, I need the energy written as

E_iaa = G_ijkl * (cos(theta_jik) - cos(theta0)) * (cos(theta_jil) - cos(theta0_prime))

where i is the common atom.

I found the same description at the end of doc page (http://lammps.sandia.gov/doc/99/force_fields.html#_cch3_930957527)

But when I look up the improper_style class2 page (http://lammps.sandia.gov/doc/improper_class2.html), the general expression is written as

E_iaa = M * (theta_jik - theta0) * (theta_jil-theta0_prime).

Likewise, I would like to express angle-angle torsion term using

(cos(theta_jik) - cos(theta0)) * (cos(theta_jil) - cos(theta0_prime)) * cos(phi)

instead of

(theta_jik - theta0) * (theta_jil-theta0_prime) * cos(phi) ( E_aat term in http://lammps.sandia.gov/doc/dihedral_class2.html)

How can I write the argument in cosine(theta) format instead of theta?

Thanks for the feedback.

Cheers,

F.S.

Hi there.

I just realize that the Angle-Angle (class II improper) and Angle-Angle-Torsion (class II dihedral) terms in LAMMPS 99 and latest version are written using theta as the argument in energy, but not cos(theta). Sorry for the misleading in previous email.

In order to tackle the desired format, is there a reasonable workaround on that, say re-write part of the source code? No need for solving the entire question but please generous guide me to the possible direction. Thanks in advance.

Cheers,

F.S.

Excuse me, but I think I know what to try. (http://lammps.sandia.gov/doc/Section_modify.html)

Thanks.