# Calculating Hydrophobic and Hydrophilic by SASA on an HPC centos cluster

**URL:** <https://gromacs.bioexcel.eu/t/calculating-hydrophobic-and-hydrophilic-by-sasa-on-an-hpc-centos-cluster/7207>\
**Category:** User discussions\
**Created:** [September 18, 2023, 6:12am UTC](https://gromacs.bioexcel.eu/t/calculating-hydrophobic-and-hydrophilic-by-sasa-on-an-hpc-centos-cluster/7207 "2023-09-18T06:12:33Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![pappo1982pl](https://avatars.discourse-cdn.com/v4/letter/p/59ef9b/32.png) [@pappo1982pl](https://gromacs.bioexcel.eu/u/pappo1982pl)\
**Post date:** [September 18, 2023, 6:12am UTC](https://gromacs.bioexcel.eu/t/calculating-hydrophobic-and-hydrophilic-by-sasa-on-an-hpc-centos-cluster/7207/1 "2023-09-18T06:12:33Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question

Hello, I have successfully run all the gromacs commands excluidng the calculation of hydrophobic and hydrophilic area by SASA. I understand that it needs to be specified by the -surface selection. I have followed the manual and wrote like this:

#### SASA

> echo 1 | singularity run --no-home -B ${PWD} --nv ./gromacs\_2018.2.sif gmx sasa -f md\_fit\_380.xtc -s md\_380.tpr -o sasa\_Hydrophobe.xvg -surface ‘group “A”’ -output ‘“Hydrophobic” group “A” and charge {-0.2 to 0.2};“Hydrophilic” group “A” and not charge {-0.2 to 0.2}’ -tu ns

However I keep getting this error:

> Error in user input:  
> Invalid command-line options  
> In command-line option -surface  
> Invalid selection ‘group’  
> Near ‘group’  
> syntax error  
> In command-line option -output  
> Invalid selection ‘group’  
> Near ‘group’  
> syntax error  
> In command-line option -output  
> Invalid selection ‘and’  
> Near ‘and’  
> syntax error  
> In command-line option -output  
> Invalid selection ‘charge’  
> Near ‘charge’  
> syntax error  
> In command-line option -output  
> Invalid selection ‘{-0.2’  
> Near ‘{’  
> syntax error  
> In command-line option -output  
> Invalid selection ‘to’  
> Near ‘to’  
> syntax error  
> In command-line option -output  
> Invalid selection ‘0.2}’  
> Near ‘}’  
> syntax error  
> In command-line option -output  
> Invalid selection ‘group’  
> Near ‘group’  
> syntax error  
> In command-line option -output  
> Invalid selection ‘and’  
> Near ‘and’