remove word repetitions for 'a'

doc/src/Section_howto.txt

@@ -2729,7 +2729,7 @@ production runs and is only required during equilibration. This way one
 is consistent with literature (based on the code packages DL_POLY or
 GULP for instance).
 
-The mentioned energy transfer will typically lead to a a small drift
+The mentioned energy transfer will typically lead to a small drift
 in total energy over time.  This internal energy can be monitored
 using the "compute chunk/atom"_compute_chunk_atom.html and "compute
 temp/chunk"_compute_temp_chunk.html commands.  The internal kinetic

doc/src/Section_start.txt

@@ -706,7 +706,7 @@ future changes to LAMMPS.
 User packages, such as user-atc or user-omp, have been contributed by
 users, and always begin with the user prefix.  If they are a single
 command (single file), they are typically in the user-misc package.
-Otherwise, they are a a set of files grouped together which add a
+Otherwise, they are a set of files grouped together which add a
 specific functionality to the code.
 
 User packages don't necessarily meet the requirements of the standard

doc/src/compute_centro_atom.txt

@@ -114,7 +114,7 @@ local defects surrounding the central atom, as described above.  For
 the {axes yes} case, the vector components are also unitless, since
 they represent spatial directions.
 
-Here are typical centro-symmetry values, from a a nanoindentation
+Here are typical centro-symmetry values, from a nanoindentation
 simulation into gold (FCC).  These were provided by Jon Zimmerman
 (Sandia):
 

doc/src/compute_stress_atom.txt

@@ -60,7 +60,7 @@ produced by a small set of atoms (e.g. 4 atoms in a dihedral or 3
 atoms in a Tersoff 3-body interaction) is assigned in equal portions
 to each atom in the set.  E.g. 1/4 of the dihedral virial to each of
 the 4 atoms, or 1/3 of the fix virial due to SHAKE constraints applied
-to atoms in a a water molecule via the "fix shake"_fix_shake.html
+to atoms in a water molecule via the "fix shake"_fix_shake.html
 command.
 
 If no extra keywords are listed, all of the terms in this formula are

doc/src/dump_modify.txt

@@ -574,7 +574,7 @@ e.g. its x-component of velocity if the atom-attribute "vx" was
 specified.
 
 The basic idea of a color map is that the atom-attribute will be
-within a range of values, and that range is associated with a a series
+within a range of values, and that range is associated with a series
 of colors (e.g. red, blue, green).  An atom's specific value (vx =
 -3.2) can then mapped to the series of colors (e.g. halfway between
 red and blue), and a specific color is determined via an interpolation

doc/src/fix_lb_fluid.txt

@@ -233,7 +233,7 @@ present, the speed of sound squared is set equal to (1/3)*(dx/dt)^2.
 Setting a0 > (dx/dt)^2 is not allowed, as this may lead to
 instabilities.
 
-If the {noise} keyword is used, followed by a a positive temperature
+If the {noise} keyword is used, followed by a positive temperature
 value, and a positive integer random number seed, a thermal
 lattice-Boltzmann algorithm is used.  If {LBtype} is set equal to 1
 (i.e. the standard LB integrator is chosen), the thermal LB algorithm