A Modern Fortran-based Parser

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This repository contains a modern Fortran-based input file parser. It uses a modified libfdf library.

Get the code

The library is included in this repository as a submodule. To clone the entire project, do

git clone --recurse-submodules https://github.com/TREX-CoE/fparser.git

Compilation

The project contains two folders (a) modified-libfdf and (b) parser.

Compile and install the modified-libfdf using the following set of commands

./configure --prefix=/usr/local FC=ifort CC=icc

make

sudo make install

In the parser folder, link the modified libfdf library with the interface Fortran file.

ifort -c m_periodic_table.F90 m_keywords.F90

ifort interface.F90 m_keywords.F90 m_periodic_table.F90 /usr/local/lib/libfdf.a

Integrate parser in your code

Just include the interface.F90 file and the keyword declaration module files in the existing Makefile of your code.

Features of the parser (including inheritance from libfdf)

Blank lines and lines starting with # are ignored.
The order of keyword-value pairs does not matter
Spaces and tabs are ignored; keyword-value pairs are parsed in a free-form.
Keywords are case insensitive.
A default value can be set for keywords not present in the input file.
Large data can be parsed using the %block structure.
Multiple keyword-value pairs can be clubbed together in a %module structure.

Syntax

Include another input file for parser to read using:

%include global.inp
Include a data file for parser to read using:

load label filename
Here, depending upon the label, parser will provide the filename. For example,

load basis cc-pvtz.gbs

Read molecular coordinates directly from the input file using

%block molecule 
12
#benzene comment
C    0.00000    1.40272  0
H    0.00000    2.49029  0
C   -1.21479    0.70136  0
H   -2.15666    1.24515  0
C   -1.21479   -0.70136  0
H   -2.15666   -1.24515  0
C    0.00000   -1.40272  0
H    0.00000   -2.49029  0
C    1.21479   -0.70136  0
H    2.15666   -1.24515  0
C    1.21479    0.70136  0
H    2.15666    1.24515  0
%endblock

Read molecular coordinates from an external .xyz file using

%block molecule < benzene.xyz

Group certain keywords using the %module construct

%module DMC
  tau     =   0.04
  etrial  = -15 Ha
%endmodule

Logical variables accept true, TRUE, T, .true. as valid keywords for True. The fdf_boolean function can also take “1” as true and “0” as false from the input.

optimize_wavefunction true
Single and Double precision numbers along with numbers in scientific format can be read using the fdf_get() function. The second number in the bracket denotes the default value.

energy_tol = fdf_get('energy_tol', 0.00001d0)
Floats/integers/strings/booleans can be parsed generically using the interface fdf_get() function. Strings are limited to 132 characters per line.

sr_tau = fdf_get('sr_tau', 0.025d0)

nspin1 = fdf_get('nspin1', 1)

opt_method = fdf_get('opt_method', "sr_n")

multiple_adiag = fdf_get('multiple_adiag', .false.)
Units can be specified to variables. Unit conversion is possible at the parsing.

If the input file has etrial = -15 Ha entry, the etrial variable can be assigned values using the fdf_physical function with unit conversion.

etrial = fdf_physical('etrial', -20.d0, 'eV')
List of public functions available for parsing the data:

Initiate

fdf_init

fdf_shutdown

Single data

fdf_get

fdf_integer

fdf_single

fdf_double

fdf_string

fdf_boolean

fdf_physical

fdf_convfac

fdf_load_filename

Lists (data enclosed in [])

fdf_islist

fdf_islinteger

fdf_islreal

fdf_list

fdf_linteger

fdf_ldouble

Returns the string associated with a mark line

fdf_getline

Test if a label is defined

fdf_defined

fdf_isphysical

fdf_isblock

fdf_load_defined

Allow to overwrite things in the FDF

fdf_overwrite

fdf_removelabel

fdf_addline

Block reading (processing each line of data)

fdf_block, fdf_block_linecount

fdf_bline, fdf_bbackspace, fdf_brewind, fdf_bclose

fdf_bnintegers, fdf_bnreals, fdf_bnvalues, fdf_bnnames, fdf_bntokens

fdf_bintegers, fdf_breals, fdf_bvalues, fdf_bnames, fdf_btokens

fdf_bboolean, fdf_bphysical

fdf_bnlists, fdf_bnilists, fdf_bnrlists, fdf_bnvlists

fdf_bilists, fdf_brlists, fdf_bvlists

Match, search over blocks, and destroy block structure

fdf_bmatch, fdf_bsearch, fdf_substring_search

fdf_setoutput, fdf_setdebug

Demonstration

In the parser folder, we have included a sample interface.F90 and m_keywords.F90 files. In the interface.F90 file, we have demonstrated how keyword-values pairs, simple data blocks, and data from external files can be read easily.

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