gpaw-python_openmpi: 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/lib64/openmpi/bin/gpaw-python_openmpi - from package: gpaw-openmpi

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

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