apbs-mergedx: 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/apbs-mergedx - from package: apbs-tools

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

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