[Pw_forum] Rigid-Body approximation with PWscf

[Sigifredo Sanchez-Carrera]

Dear PWscf users,

I was wondering if the "rigid-body approximation" can be explicitly treated with
PWscf. I am trying to set a lattice dynamics calculation of molecular organic
crystals, within the rigid-body approximation in which the molecules are
constrained to maintain their equilibrium intramolecular bond lengths and bond
angles.

I have seen examples in which you can actually set either an atomic position
(example 1) or the distance & angles between atoms (example 2). My molecular
systems include 40 – 50 atoms per unit cell, thus several constrains in terms of
bonds and angles are required; I would be interested in knowing if this approach
can be fulfilled with PWscf according to your experience, and what are the
general guidelines to implement it?

Thanks in advance,
Sigifredo Sánchez-Carrera


===================
Example 1:

ATOMIC_POSITIONS { bohr }
C        0.000000000   0.000000000   0.000000000  0 0 0
C        2.100000000   0.000000000   0.000000000
H       -1.600000000   0.400000000   0.000000000
H        3.600000000  -0.400000000   0.000000000
===================


===================
Example 2:

ATOMIC_POSITIONS { bohr }
C        0.000000000   0.000000000   0.000000000  0 0 0
C        2.100000000   0.000000000   0.000000000
H       -1.600000000   0.400000000   0.000000000
H        3.600000000  -0.400000000   0.000000000

CONSTRAINTS
2  1.D-8
planar_angle  1  2  4
distance  1  2
===================


--
Sigifredo Sanchez-Carrera

Georgia Institute of Technology
School of Chemistry and Biochemistry
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Atlanta, GA 30332-0400

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