GMXRC: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/GMXRC - from package: gromacs-common

You may install the required package with command yum install {package}

Error in other languages:
GMXRC: bevel nie gevind nie
GMXRC: comandă negăsită
GMXRC: comando não encontrado
GMXRC: commande introuvable
GMXRC: command not found
GMXRC: käsku ei ole
GMXRC: không tìm thấy lệnh
GMXRC: komanda nerasta
GMXRC: Kommando nicht gefunden.
GMXRC: kommandot finns inte
GMXRC: komut yok
GMXRC: nie znaleziono polecenia
GMXRC: níor aimsíodh an t-ordú
GMXRC: no se encontró la orden
GMXRC: no s'ha trobat l'ordre
GMXRC: opdracht niet gevonden
GMXRC: parancs nem található
GMXRC: perintah tidak ditemukan
GMXRC: príkaz nenájdený
GMXRC: příkaz nenalezen
GMXRC: команда не найдена
GMXRC: командата не е открита
GMXRC: 命令找不到
GMXRC: コマンドが見つかりません